This dataset is a comprehensive, global compilation of
published uranium–thorium (U-series) dated fossil coral records from
Uranium–thorium (U-series) dating of Last Interglacial (LIG) fossil corals has long been a key component of the paleoceanographic toolkit. Early work utilized alpha spectrometry, which has analytical uncertainties on the order of several thousand years for LIG fossil corals. Nonetheless, these early studies provided some of the first radiometric age constraints on the timing of Late Pleistocene glacial–interglacial cycles and were critical for validating the Milankovitch hypothesis (e.g., Broecker et al., 1968; Bender et al., 1979). More recently, the advent of modern mass spectrometric U-series techniques in the mid-1980s reduced analytical uncertainties of LIG fossil coral U-series ages to 1000 years (1 kyr) or less, allowing workers to precisely determine the timing of the LIG and further refine our understanding of the relationship between orbital forcing, solar insolation, and sea-level/climate change (Chen et al., 1986; Edwards et al., 1987a, b; Gallup et al., 1994; Stirling et al., 1995, 1998). In the last 3 decades, further improvements to existing thermal ionization mass spectrometry methods and the development of robust inductively coupled plasma mass spectrometry techniques have continued to push the boundaries of analytical precision, and today many labs routinely generate coral U-series ages with an analytical precision of several hundred years for the LIG (e.g., Cheng et al., 2000; Stirling et al., 2001; Andersen et al., 2008; McCulloch and Mortimer, 2008; Cheng et al., 2013).
Global synthesis studies have estimated that the LIG sea-level highstand lasted from approximately 129 to 116 thousand years ago and that global mean sea level (GMSL) was likely 6–9 m higher than at present (Kopp et al., 2009; Dutton and Lambeck, 2012; Masson-Delmotte et al., 2013; Dutton et al., 2015a). However, the rate, timing and magnitude of GMSL change within the LIG is still debated, with published interpretations ranging from a single, stable highstand peak to multiple peaks separated by ephemeral sea-level falls (Kopp et al., 2017, and references therein). Reconciling these different interpretations for how sea level evolved during the LIG is crucial for improving our understanding of ice sheet (in)stability during warm periods such as the present Holocene interglacial and for constraining the future sea-level response to human-caused climate change.
Understanding what the global fossil coral record tells us about LIG sea
level requires careful interpretations of the age, elevation and underlying
metadata that comprise a coral relative sea level (RSL) indicator. This is
not a trivial undertaking, as data reporting protocols vary by research
group and have evolved over the 30
Here we present, to our knowledge, the most comprehensive compilation to
date of U-series-dated fossil coral RSL indicators for the LIG as a
contribution to the World Atlas of Last Interglacial Shorelines (WALIS,
A site map of all the localities included in the database is provided in Fig. 1. The dataset includes 1312 individual U-series measurements and 104 fields
for a total of 136 448 entries. All included U-series ages are (1) dated to between 150–110 kyr and/or (2) derived from a coral colony that
was sampled from an LIG fossil reef unit. U-series ages and isotope ratios
were recalculated using the most recent set of decay constants for
Site map of U-series-dated fossil corals compiled for this study. Sites are differentiated based on regional tectonic setting, with stable sites marked with a cyan circle, subsiding sites with a purple triangle and uplifting sites with an orange square. Map created using GMT v5.4.5 (Wessel et al., 2013).
We preserved the originally reported values and metadata within WALIS, while
also producing two pre-screened, interpreted versions of the dataset based
on data quality that can assist users with identifying fossil coral U-series
dates that display open-system behavior. The intention is that this combined
approach will ensure that this dataset will adhere to FAIR data principles,
being findable; accessible; interoperable; and, above all, reusable
(Wilkinson et al., 2016). This dataset is
open source, and the most recent version can be found at
This data compilation is one component of the WALIS project, which seeks to
document all previously published geologic and chronostratigraphic
constraints on RSL during the LIG. Although the primary focus of our
contribution is on the U-series aspect of the fossil coral record, this
information is inseparable from the elevation information and associated
metadata when reconstructing RSL at fossil reef sites. A U-series-dated
fossil coral can be used as an RSL indicator, provided that certain criteria
are met. In a recent review, Rovere
et al. (2016) proposed that an RSL indicator has three key components:
the indicator's position, both in terms of geographic coordinates and
relative to an established height datum; the indicator's position relative to local sea level at the time it was
deposited; and some form of radiometric or chronostratigraphic age constraint on the timing
of deposit formation.
If a coral with a U-series age has been collected in primary growth position
and meets criteria 1 and 2, then the coral is considered an RSL indicator.
In the absence of paleowater depth information (i.e., the sample does not meet
criterion no. 2), corals are generally considered as marine limiting because
most coral taxa are limited to below mean lower low water/mean low water
springs (MLLW/MLWS), although certain coral taxa and growth forms can
colonize the intertidal zone. Hence, in the absence of any additional
paleoenvironmental context, sea level is considered to have been at or above
the elevation of the top of the coral colony. Fossil coral RSL indicators,
however, are most useful when the depth at which the coral was growing is known
(see Sect. 2.4).
Identification of reliable fossil coral RSL indicators requires careful vetting of each sample's age (i.e., diagenetic screening) and vertical position relative to past sea level. This is important because ignoring additional relevant observations and metadata can result in erroneous conclusions about past sea-level change. In this compilation, we included new paleowater depth interpretations, as well as several screening “scenarios” that were designed to screen out altered samples using a consistent set of defined criteria. These screening scenarios are not intended to be the final word on which coral samples should be accepted/rejected in future studies. Rather, our twin objectives here are (1) to highlight best practices when interpreting fossil coral RSL data and (2) to provide curated example datasets that are immediately available to WALIS users seeking a current best estimate of interpreted RSL in space and time using the coral data. We caution that the screened datasets presented here may not identify every open-system coral, so even U-series ages that pass a particular closed-system criterion still need to be evaluated in the context of existing geologic/sedimentary evidence to assess whether the age is meaningful. In other words, this screening process is only the first step in interpreting the sea-level history based on fossil coral data. Additional stratigraphic, sedimentologic or other metadata may provide justification to modify or reject these preliminary age interpretations. Below, we explain the method we used to develop these datasets and also briefly address the effects of tectonics, glacial isostatic adjustment and dynamic topography on solid-earth displacement, which can cause substantial departures in RSL relative to GMSL.
A simplified overview of the WALIS U-series fossil coral dataset and
workflow is provided in Fig. 2, and the database field descriptors can be
found here:
Simplified flowchart of WALIS coral U-series database structure. All coral age, elevation and metadata are included in the “U-series” component of the database, whereas the “fossil coral RSL” database only includes entries from corals that are in primary growth position.
This dataset contains several new features that have been added since the
Dutton and Lambeck (2012) and Hibbert et al. (2016) compilations. Several
key updates are as follows:
New sample identifiers are included, which make it easier to identify which U-series
analyses are associated with the same coral colony. Sample IDs are reported
in the format Sample elevations are now reported both in meters above mean sea level
(a.m.s.l.) and relative to MLLW/MLWS. In cases where a proximal tide gauge datum was not available,
this conversion was done using the IMCalc software package of Lorscheid and
Rovere (2019). All color coding from the Hibbert et al. (2016) database has been removed.
This information is now stored in the “comment” columns. The columns for reporting coral taxonomic information have been revamped to
allow entry of family, genus and species information for each coral sample.
Coral taxa were updated to reflect the most recent taxonomic classification
as reported by the World Register of Marine Species (WoRMS, All U-series ages from transported corals are now marked as not in primary
growth position, even if the original publication explicitly states that the
sample is in situ (e.g., an in situ clast/conglomerate). We have back-calculated U-series activity ratios, when possible, that were
not reported in the original publication and had not already been done by
Hibbert et al. (2016). As with Hibbert et al. (2016), all ages and activity ratios, where
appropriate, have been recalculated using the Cheng et al. (2013) decay
constants for We have restored some of the original information and comments from Dutton
and Lambeck (2012) that were not included in the Hibbert et al. (2016)
compilation. Locality information for Barbados reef terraces have been standardized and
reformatted in cases where there were multiple names for the same site.
Corals precipitate their skeletons directly from dissolved ions in seawater,
forming a calcium carbonate mineral called aragonite. As part of this
process, uranium (U) is incorporated at parts-per-million
concentrations as impurities within the aragonite crystal lattice, and in
ideal, closed-system conditions thorium (Th) concentrations are negligible.
This is because of the high particle reactivity of Th, which causes the
element to have a relatively short residence time in the water
column. Once the coral skeleton has formed, the U-series radiometric clock
is effectively started, and the elapsed time is measured by the ingrowth of
Unfortunately, coral skeletal material is also highly susceptible to
post-depositional alteration (i.e., diagenesis), particularly after exposure to
meteoric waters, as is often the case with emergent LIG reef units
(Thompson et al., 2003). As a result, a
U-series
Examples of open-system behavior from LIG fossil coral
U-series data.
Several models have been proposed to correct U-series ages that display open-system behavior, but it is well understood that patterns of diagenesis in altered corals at a study site follow multiple diagenetic pathways that cannot be explained by a single model (Henderson and Slowey, 2000; Scholz et al., 2007; Thompson et al., 2003; Villemant and Feuillet, 2003). While there are circumstances in which altered coral samples may be good candidates for open-system correction, this would require further analysis of diagenetic trends at each site, which is beyond the scope of this study, as no single open-system model can explain all of diagenetic variability in the dataset. For example, the Thompson et al. (2003) open-system model is well suited to correct diagenetic arrays common to Barbados and some localities in Western Australia. It does not, however, explain all modes of diagenesis present in the fossil coral record (e.g., Figs. 3a, 4). Hence, this analysis focuses on assessing closed-system ages.
Open-system model of
Thompson et al. (2003) applied to
U-series measurements from Seychelles sample DU15-010 from Fig. 3a
(Dutton et al., 2015b). In this case, the
diagenetic array is roughly perpendicular to the open-system isochrons, so
the open-system correction does not change the high degree of age
variability within this coral colony (
Previous studies typically adopted a set of geochemical screening criteria
to remove U-series data that have been altered through open-system behavior
(e.g., Scholz
and Mangini, 2007). Three of the most common geochemical variables used are
calcite content; detrital
For each published data source, the original list of ages that were
accepted/rejected by the study authors is recorded in WALIS. It is often
difficult to directly compare screened data between different publications
and research groups, as the specific screening criteria applied can vary
substantially from study to study. As a result, previous global fossil coral
compilations (Dutton and Lambeck,
2012; Hibbert et al., 2016) have applied these screening criteria uniformly
across the entire dataset to ensure that only the most geochemically
pristine samples were used for sea-level interpretations. Applying a blanket
screening criterion, however, results in the vast majority of U-series
analyses being rejected and ignores differences that may exist in the nature
of diagenesis at different sites and with different coral taxa. Therefore,
we applied two sets of screening protocols to the dataset: (1) a “strict”
protocol that applies uniform screening cutoffs to each U-series age based
on the three geochemical variables listed above and (2) a “flexible”
protocol that allows for site- and sample-specific criteria, particularly
where multiple subsamples of the same coral have been dated.
The strict screening protocol follows the general approach of
Dutton and Lambeck (2012) and
Hibbert et al. (2016), with some modification in the case where multiple
subsamples from a single coral specimen were dated. To be accepted, a sample
must have
calcite content detrital
If any of these values are not reported or cannot be calculated, the
U-series age is rejected. Additionally, in the case where multiple
subsamples of the same coral pass the strict screening criteria, the ages
must also be reproducible (i.e., overlap or nearly overlap within analytical
uncertainty) and not lie along a diagenetic array (e.g., Fig. 3). Although this
last stipulation regarding age reproducibility is necessary to evaluate
corals with multiple dated subsamples properly, it has the consequence of
biasing the dataset towards corals that have only been dated once but pass
the screening criteria. Ideally, we would only use fossil coral ages that
have been reproduced by multiple subsamples as RSL
indicators, to ensure that multiple subsamples from the same coral specimen
yield reproducible ages. However, this was not feasible for the dataset
considered here, as it would have required rejection of nearly all the coral
data that were compiled. Although the application of uniform screening
criteria to the global dataset is appealing from a logistical perspective
and gives the appearance that data are being treated equally, there can be
important methodological differences and additional contextual information
that cannot be incorporated using a uniform screening protocol. To address
this, we also applied a flexible screening protocol that evaluates each
study and study site independently, so that nuances in U-series age
interpretations could be evaluated.
Many screening decisions are context based and were addressed separately for each site, but some general modifications to the strict screening protocol are addressed here. First, we expanded the calcite screening threshold to include all corals that are below the limit of quantification for the XRD method employed, which can be as high as 4 or 5 % for some studies.
Second, we allowed for a higher
Finally, we expanded the upper limit of the
The purpose of these screening protocols is, specifically, to identify the
highest-quality closed-system fossil coral U-series ages that can be used to
provide constraints on sea-level change
Even if a fossil coral is associated with a robust U-series age, it cannot be treated as an RSL indicator if the vertical position of the sample relative to paleo-sea-level is not known. This cannot be determined if a coral has been reworked as a cobble or clast since it is not known where the sample originally grew. Therefore, only a fossil coral that has not been transported (i.e., is in primary growth position) can be considered an RSL indicator.
Determining whether a coral sample is in growth position from legacy data can be challenging. The reporting criteria used are not standardized across the literature, and even the terminology used can vary from paper to paper, if it is addressed at all. Generally speaking, the two most common expressions used to indicate that a coral is in place are “growth position” and “in situ”. Growth position is usually interpreted as expressing greater confidence than in situ, as it implies that the coral is in the correct growth orientation or that a clear basal attachment to the reef substrate is visible at the outcrop scale. For the present study, however, we accepted corals with either designation as an RSL indicator. Hereafter, corals that are listed as either in situ or growth position will be colloquially referred to as in “primary growth position”.
There are two unique circumstances for which additional information is required to determine if a coral is in primary growth position. First, some studies refer to a coral specimen as being in primary growth position, yet the depositional context given clearly indicates that the coral has been reworked (e.g., “in situ clast” or “in situ conglomerate”). We interpreted such samples as not being in primary growth position. Second, we accepted the designation of “coral framework” as equivalent to in situ, and therefore primary growth position, for samples that were collected via drill core (e.g., Camoin et al., 2001; Thomas et al., 2009; Vezina et al., 1999), because in these cases it was impossible to explore the sample's relationship to the rest of the reef unit. It is important, however, to recognize that it is possible for coral colonies to have been transported but still appear to be in primary growth position. For example, there are three samples from Stein et al. (1993) collected in Papua New Guinea (sample IDs ST93-003, ST93-004 and ST93-014) that are reported as being in growth position but are ultimately derived from detached limestone blocks and, therefore, were not treated as primary-growth-position corals. In some cases, this additional context is not provided in the published literature, and reappraising the existing stratigraphic evidence at certain field cites may be warranted (e.g., Skrivanek et al., 2018). However, such an a posteriori assessment is outside the scope of this study and the WALIS special issue.
After determining that a coral sample has a reliable U-series age and is in primary growth position, the final challenge involves determining the paleowater depth uncertainty for the coral. As a primary-growth-position coral, we know that the sample is, at minimum, marine limiting, as corals from the highest growth position at an LIG fossil reef site did not necessarily grow directly beneath the paleo-sea-surface. Many of the studies included in our compilation rely on modern analogue studies of present-day reef ecology to constrain paleowater depth uncertainties.
There are two primary techniques that use the modern analogue approach to constrain paleowater depth (Fig. 5). The first technique is an assemblage-based approach, which examines a series of variables such as coral taxa/growth forms present, associated coralline algal species and relevant sedimentary context to identify the most probable depth range for the reef unit in which the coral grew (Abbey et al., 2011; Cabioch et al., 1999; Dechnik et al., 2017; Lighty et al., 1982). The assemblage approach is a powerful tool that can substantially reduce the paleowater depth uncertainty for LIG fossil reef sites. Assigning paleowater depth ranges based on fossil reef assemblages does, however, involve a certain degree of subjectivity. Therefore, users of assemblage-derived paleowater depth ranges should be aware that these interpretations may change after a study's original publication date if new stratigraphic context and more robust modern and/or paleoecological studies become available. These are included to help define the paleowater depth uncertainty where possible.
Comparison of approaches for interpreting sample
paleowater depth based on modern coral depth distributions and reef
assemblages for LIG fossil reef outcrops in the Seychelles. Modern depth
distributions for the genera
A second approach relies upon modern coral depth distributions to
parameterize paleowater depth uncertainty
(e.g., Hibbert et al., 2016). A significant drawback
of using modern depth distributions is that relying upon the full range of
growth can greatly overestimate the true depth relative to actual paleo-sea-level position, as many corals can grow in a wide range of water depths.
For example, individual colonies of the Caribbean coral species
Whenever possible, we used assemblage-derived paleowater depth estimates, which came from either the original publication or reinterpretations from a subsequent study. If no paleowater depth constraints were available, then we applied the taxon-based modern water depth distributions instead (i.e., the median, upper and lower water depth limits for the 95 % confidence level from OBIS, 2014). All paleowater depth interpretations are current as of the date of publication, but users are cautioned that some of these interpretations will likely need to be revisited in the future as new studies advance our understanding of LIG and modern reef ecology.
It should also be noted that in the online WALIS database template there are
three values that must be given when assigning paleowater depth: (1) estimated paleowater depth and the (2) upper and (3) lower limit of this depth
estimate. In the user interface, the upper depth limit is listed first,
followed by the estimated paleowater depth and lower limit, with all depths
entered as negative numbers. The estimated paleowater depth does not
necessarily have to be the midpoint of the interpreted depth range (e.g., a coral
collected from an
In general, site-specific fossil reef RSL histories for the LIG diverge from GMSL because of processes such as regional tectonics, glacial isostatic adjustment (GIA) and dynamic topography (Broecker et al., 1968; Farrell and Clark, 1976; Mitrovica and Milne, 2003; McMurtry et al., 2010; Austermann et al., 2017). Although correcting fossil coral RSL records for these processes was not the main focus of this study, it is nonetheless important for a user to be cognizant of this complication when comparing sea-level records from different sites. It is also worth keeping in mind that, although all three factors affect the uncertainty in the absolute elevation for coral-derived RSL reconstructions, the relative contribution of each varies from site to site.
Many of the seminal studies that utilized fossil coral RSL data come from uplifted fossil reef terraces such as those found in the island nation of Barbados and on the Huon Peninsula in Papua New Guinea (Broecker et al., 1968; Bender et al., 1979; Edwards et al., 1987a; Stein et al., 1993). These sites were targeted largely because the uplifted terraces facilitated easy sampling of core material without the need for scientific drilling and because the exposed outcrops enabled detailed facies analysis of the fossil reef morphology and paleoecology. In contrast, some locations in the WALIS database have experienced subsidence since the LIG. In many cases, these sites are located on volcanic hot-spot islands which are subsiding because of crustal loading (e.g., Camoin et al., 2001; Thomas et al., 2009).
The challenge of interpreting RSL records at tectonically active study sites
is that the uplift rate must be well constrained to extract meaningful
information about GMSL change. In many cases, previous workers estimated
uplift/subsidence rates using the highest-growth-position coral from an LIG
unit (e.g., McMurtry et al., 2010). The
general formula used to correct for tectonic activity is
Values used for
The advance and retreat of large continental ice sheets during the last glacial cycle caused long-lasting, global perturbations to the Earth's gravity field and rotation that persist to this day (Farrell and Clark, 1976; Mitrovica and Milne, 2003). This phenomenon, called glacial isostatic adjustment, can cause meter-scale changes in RSL at fossil reef sites that must be addressed to extract meaningful GMSL information for fossil coral sea-level indicators (Dutton et al., 2015a). Indeed, the 6–9 m estimate for the peak magnitude of the LIG highstand has been inferred from global compilations of RSL records that were corrected for GIA effects (Dutton and Lambeck, 2012; Kopp et al., 2009).
The magnitude of the difference between RSL and GMSL at fossil reef sites is
spatially variable, depending in part on the proximity to past continental
ice sheets. For instance, GIA modeling predicts a gradient in RSL across
the circum-Caribbean region, as many of the sites were sitting atop or
proximal to the peripheral bulge of the Marine Isotope Stage (MIS) 6 ice
sheet that covered North America (Dutton and
Lambeck, 2012). This is supported by recent field surveys from The Bahamas,
which revealed a
Dynamic topography is vertical displacement of the solid earth caused by mantle convection. Previous work demonstrated that the effect of dynamic topography on million-year timescales is of a similar order of magnitude to apparent changes in GMSL inferred from RSL records (Moucha et al., 2008; Müller et al., 2008; Rowley et al., 2013). Recent work demonstrated that this is also the case for the LIG, in that dynamic topography can cause meter-scale differences in RSL between the LIG and the present day at some localities (Austermann et al., 2017). These studies clearly demonstrate that the effect of dynamic topography on LIG RSL records is nontrivial, and further work is needed to assess how mantle dynamic topography may affect interpretations of past sea level from fossil reef sites.
In summary, there are both local (tectonic) and global-scale (GIA, dynamic topography) processes that can cause RSL at a fossil reef site to depart from the global mean, and they must be accounted for to extract a robust GMSL signal using U-series ages and elevations of fossil corals. Although GIA and dynamic topography influence interpretation of RSL compared to GMSL, we do not provide those interpretations here. Instead, this study was undertaken to define RSL at each site so that robust RSL interpretations are available that can be used to constrain such processes and, by extension, GMSL.
An overview of the coral U-series ages available in the dataset is included
below, organized alphabetically by geographic study area. Each entry, where
appropriate, contains the following:
the total number of U-series ages available for the study area and the
number of unique coral specimens dated; whether any of the corals were dated in duplicate, triplicate, etc.; how many ages were accepted by the original publication; how many ages (if any) pass the flexible and strict screening protocols; identification of corals that pass screening and are in primary growth
position; mention of previous interpretations of paleowater depth uncertainty and what
water depth uncertainties were assigned by the present study; whether the site is tectonically uplifting, subsiding or stable; and whether the U-series ages have been discussed by other contributions to the
WALIS special issue with regards to the broader geologic context at each
locality.
A summary of the coral U-series ages that passed the strict and flexible
screening protocol is provided in Supplement S1, and the flexible
protocol is also coded into WALIS as the preferred screening protocol
utilized in this paper.
In total, 141 U-series ages were accepted from 104 unique coral samples that passed the strict screening protocol, whereas 286 ages from 215 samples were accepted under the flexible protocol (Table 1). Of the samples that were treated as RSL indicators, 59 ages were accepted from 39 coral samples under the strict protocol, whereas 150 ages from 112 coral samples were accepted under the flexible protocol. Finally, for the marine-limiting samples, four ages from three coral samples were accepted under the strict protocol, whereas nine analyses from eight coral samples were accepted under the flexible protocol. We did not include coral U-series ages that were measured using the considerably less precise dating method of alpha spectrometry, but the ability to add alpha dates is present in the WALIS user interface. The addition of alpha spectrometry ages to this dataset by community members is encouraged, especially for sites where mass spectrometric U-series measurements are not available.
Summary of samples that passed closed-system screening protocols.
Corals were U-series-dated from emergent LIG reef deposits on Great Inagua,
San Salvador and the Abaco Islands in The Bahamas
(Chen
et al., 1991; Hearty et al., 2007; Thompson et al., 2011). A total of 200
U-series ages from 142 unique coral specimens were reported, with 29 of
these corals dated at least in duplicate. In total, the original study
authors accepted 49 U-series ages from 37 coral samples as closed-system
ages. Thompson et al. (2011) did not use
closed-system ages and instead applied an open-system correction to each
sample. Under the strict screening protocol, 35 U-series ages from 26 coral
samples were accepted. This number increased to 43 U-series ages from 29
corals when the flexible screening protocol was applied. Sample ages that
passed flexible screening ranged from 131.3
Several site-specific adjustments were made under the flexible screening
protocol. First, the
Assessing whether corals from The Bahamas dataset were in primary growth
position is challenging. Chen et al. (1991) applied the
term “in situ” to describe both growth position corals that are part of the reef
framework and detrital coral rubble that had been cemented in place. For the present compilation, we categorized
all corals derived from rubble layers as “not in primary growth position”. Using
this approach, a total of 14 ages from Chen et al. (1991), derived from 11 coral specimens, can be treated as RSL indicators
under the flexible screening protocol. Previous workers assigned a
paleowater depth range of 3 to 4 m for the Cockburn Town and Devil's Point
sites (Chen et al., 1991). A more recent study, however,
reevaluated the vertical position and facies characteristics of the two
fossil coral reefs using high-precision surveying techniques and published
new paleowater depth interpretations (Skrivanek et al.,
2018). It is difficult to compare the present dataset to the reef zones
described in Skrivanek et al. (2018), as
Chen et al. (1991) did not distinguish between reef units
in their study. All of the corals in primary growth position, however, were
colonies of
Thompson et al. (2011) distinguished corals that were
derived from a rubble layer from those collected from the in situ reef framework but
gave no elevation information associated with each sample, so none of the
samples are used as RSL indicators here. Though elevation estimates were
provided in Thompson et al. (2011) for each reef unit, these elevations do
not always match those subsequently surveyed at the same sites, calling into
question the use of those approximate elevations (Skrivanek et al., 2018).
Primary-growth-position corals can, however, still be used to constrain the
maximum age of each fossil reef, even without published elevation data. A
total of five corals (11 analyses in total) from
Thompson et al. (2011) are in primary growth position
and passed the flexible screening criteria. These ages range from 127.3
U-series coral ages were reported for three locations along the Pacific coast of Baja California, Mexico (Muhs et al., 2002a). Corals collected for that study came from detrital sedimentary deposits on marine terraces and, therefore, were not in primary growth position and cannot be used as strictly reliable RSL indicators. Instead, the study authors used coral U-series ages as a constraint on the maximum age of the terraces. In total, 26 corals were dated, and the study authors accepted 16 of the U-series ages. None of these ages passed the strict or flexible closed-system criteria.
Barbados is one of the most intensely studied LIG fossil reef localities in
the world, with 141 U-series analyses reported for 107 corals from 11
separate studies
(Bard
et al., 1990; Blanchon and Eisenhauer, 2001; Cutler et al., 2003; Edwards et al.,
1997, 1987b; Gallup et al., 1994, 2002; Hamelin et al.,
1991; Muhs and Simmons, 2017; Speed and Cheng, 2004; Thompson et al., 2003).
The island is located on an accretionary prism and has experienced
differential uplift since the LIG. Local uplift rates vary from
Of the U-series ages reported, the original study authors accepted 40 ages
from 33 unique coral specimens. It should be noted that
Thompson et al. (2003) did not apply
closed-system screening criteria; rather, an open-system model was used.
Under the strict screening protocol, a total of 24 U-series ages were
accepted from 17 corals, whereas the flexible protocol accepted 41 ages from
28 corals. Ages from the flexible screening protocol range from 103.8
Of the samples that passed flexible screening, a total of eight U-series
ages (six corals in total) came from corals that were stated as being in
primary growth position, with ages ranging from 103.8
LIG-aged corals are present at Grape Bay on the southern side of Bermuda
(Ludwig et al.,
1996; Muhs et al., 2002b). These deposits are inferred to be originally
derived from patch reefs but are not in primary growth position and may
have been storm derived (Muhs et
al., 2002b). Therefore, the ages presented in these studies represent a
constraint on the maximum age of the rubble deposit but cannot be used as
RSL indicators. In total, nine corals were dated from Grape Bay, and the
authors originally accepted seven of the ages. Only two corals pass the
strict closed-system criteria: MU02-019, with an age of 116.9
Several studies reported U-series coral ages from marine deposits along the
southwest coast of California and several of the Channel Islands
(Muhs
et al., 2012a, 2006, 2002b; see global review of MIS 5a/c sea-level records by
Thompson and Creveling (2021) for an overview of MIS 5 marine
terraces along the California coast). These samples are solitary
Two LIG ages are reported from Gran Canaria and Lanzarote in the Canary
Islands (Muhs
et al., 2014). Both corals were
Zazo et al. (2007) reported
U-series coral ages that were used to constrain the age of marine terrace
conglomerates on Sal Island, Cabo Verde. In total, 10 U-series ages were
reported for five corals (and one hydrozoan), with one coral sample
(ZA07-004) analyzed five times. All coral ages were accepted by the study
authors, but only one age from coral ZA07-004 (129.5
U-series ages have been reported for multiple outcrops of the LIG Hato unit
on the island of Curaçao, for a total of 25 ages from 15 unique coral
colonies
(Hamelin
et al., 1991; Muhs et al., 2012b; for a regional overview, see Rubio-Sandoval
et al., 2021). Curaçao is slowly uplifting, with an estimated uplift
rate of 0.026 to 0.054 m/kyr, based on the “highest inner edge” elevation
of the Hato unit at 12.4 m (Muhs et al., 2012b). In total, the study authors
accepted five U-series ages from four unique coral specimens. Under the
strict screening protocol, this is reduced to a single age of 118.8
All samples which passed the flexible screening criteria were in primary
growth position. Based on the paleoenvironmental interpretations of Muhs et
al. (2012b), samples SC78-005 and MU12-001 were part of an
Fossil corals of LIG age were reported for the Abdur Reef Limestone on the Red Sea coast of Eritrea (Walter et al., 2000). The Eritrean coast is tectonically active and is estimated to be uplifting by 0.06 m/kyr based on the elevation of the LIG reef deposits (Hibbert et al., 2016). In total, seven U-series ages were reported for six corals, with one coral dated in duplicate. In the original study, the authors accepted all ages, except for one from coral WA00-006, which had anomalously low U content and an age that was older than expected. None of the ages passed the strict or the flexible closed-system screening criteria.
Fossil corals have been dated from multiple sites across the Florida Keys
(Fruijtier
et al., 2000; Muhs et al., 2011; Multer et al., 2002). In total, 55 U-series
ages were reported for 51 unique coral samples, with four corals dated in
duplicate. In total, the study authors accepted 15 of the ages from 13 coral
samples. Under the strict screening criteria, four ages were accepted from
three unique coral specimens from Windley Key: MU11-026, with a weighted
mean age of 115.1
All 10 corals that passed the flexible screening protocol were in primary
growth position and, therefore, can be used as RSL indicators. These samples
were collected from outcrops of the Key Largo Limestone at Windley Key and
Key Largo, with sample elevations ranging from 2–5 m a.m.s.l. (Muhs et al., 2011). The
dominant coral taxa in the outcrops studied at both localities were massive
We adopted the 3 m estimate of
Muhs et al. (2011) as the most
probable paleowater depth for the LIG deposits at Key Largo and Windley Key
and further parameterized the possible range of paleowater depths. As stated
by Muhs et al. (2011), the optimum
water depths for
A regional overview of LIG sea-level records for French Polynesia is
provided by Hallmann et al. (2020). Many of the islands and archipelagos in
French Polynesia are former hot-spot volcanoes that are subsiding because of
volcanic loading. In these cases, LIG deposits are often located below sea
level and can only be accessed via scientific drilling. U-series ages from
corals have been published from two locations in French Polynesia: Mururoa
atoll in the Tuamotu Archipelago and offshore drilling at Tahiti during IODP
Expedition 310 (Camoin et al., 2001; Thomas et al., 2009). Both Mururoa
Atoll and Tahiti have been subject to subsidence since at least the Late
Pleistocene. The subsidence rate at Mururoa was estimated to be
The existing dataset for French Polynesia contains 19 U-series dates from 12
corals, with five corals from Tahiti dated in duplicate and one in
triplicate. Of the six corals analyzed from Mururoa, only one age (CA01-007)
was accepted by the study authors. This sample also passed the strict
screening protocol and has a recalculated age of 126.0
Sample CA01-007 from Mururoa was reported as being “reworked”
(Camoin et al., 2001).
Samples TH09-001, TH09-003, TH09-005 and TH09-008 are both interpreted as
being in growth position and thus can be used as RSL indicators. TH09-003
and TH09-008 are both massive
Fossil corals have been dated from multiple localities across Grand Cayman (Coyne et al., 2007; Vezina et al., 1999). In total, 15 corals from the LIG and late MIS 6 were dated, with the authors accepting all but three ages. All of the ages were rejected by the strict and flexible closed-system screening protocols.
Two studies have reported LIG U-series ages from the Great Barrier Reef,
which were collected via scientific drilling on modern reef flats
(Braithwaite et al., 2004; Dechnik et
al., 2017). A total of 40 ages from 14 unique coral specimens were reported,
and the authors originally accepted 11 of the ages from five corals. All but
one of these corals (BR04-001) were dated in triplicate. Under the strict
screening protocol, three ages were accepted from two coral samples
(DE17-001, DE17-003). When the flexible protocol was applied, the total
number of accepted ages expanded to include seven ages from three corals:
DE17-001, with a weighted mean age of 128.7
All three corals that passed the flexible screening protocol were in primary growth position and can be used as RSL indicators. Using the coralgal assemblage interpretations, Dechnik et al. (2017) assigned these samples a 0–6 m paleowater depth range, which we also adopted.
One study reported corals with LIG ages from uplifted terraces on the
Perachora Peninsula, Greece, which were originally used to constrain local
uplift rates (Dia et al., 1997). The authors
reported that the two corals with LIG ages (DI97-002, DI97-003) showed signs
of open-system behavior, based on uranium isotopes (
Three studies reported U-series ages on corals from uplifted terraces along
the Gulf of Aqaba
(Bar
et al., 2018; Manaa et al., 2016; Yehudai et al., 2017).
Bar et al. (2018) inferred an
uplift rate of 0.13 m/kyr for the northeastern Gulf of Aqaba based on the
present-day elevation of the coral terraces and the timing of diagenesis for
altered fossil corals dated by
Yehudai et al. (2017). In total,
67 U-series ages were reported for 18 unique coral specimens, with the
majority of samples dated in triplicate or greater. In total, the study
authors accepted six of these ages from four coral samples. Under both the
strict and flexible closed-system screening criteria, only two samples were
accepted from the upper Haql terrace: MA16-003, with an age of 119.7
It is unclear which coral samples were collected in primary growth position, so MA16-003 and MA16-004 were not treated as RSL indicators within the database.
Bard et al. (1990) reported U-series ages from the
northwest coast of Haiti. In total, three analyses were conducted on two
unique coral specimens, with one of the corals dated in duplicate. All three
ages were accepted by the study authors, but detrital Th content was not
reported, which meant we were unable to accept the ages based on the strict
screening protocol. Under the flexible protocol, all three ages were
accepted from two corals: BA90-021 (122.8
Several studies have published coral U-series ages from the Waimanalo
Formation on the Hawaiian island of Oahu, which dates to the LIG
(Hearty
et al., 2007; McMurtry et al., 2010; Muhs et al., 2002b; Szabo et al., 1994;
for a regional overview, see Hallmann et al., 2020). Oahu is slowly uplifting
at a rate of
In the original studies, the authors accepted 59 ages from 52 coral samples,
whereas under the strict screening protocol we accepted 25 U-series ages
from 23 coral samples. Using the flexible screening protocol, this number
increased to 34 ages from 29 coral samples, with ages ranging from 110.84
Coral U-series ages were reported for two locations in Indonesia: Sumba
Island and Southeast Sulawesi
(Bard
et al., 1996; Pedoja et al., 2018; see Maxwell et al., 2021, for a regional
overview). Both locations are tectonically active, with uplift rates for
Sumba Island and Southeast Sulawesi estimated by the study authors to be 0.2–0.5 and 0.12–0.29 m/kyr, respectively. Between these two study
sites, a total of 21 corals were dated, and 14 of these ages were accepted
by the study authors. Based on the strict closed-system criteria, four of
the ages from Pedoja et al. (2018) were accepted: PE18-001, with an age of 133.7
Although sample elevations for
Pedoja et al. (2018) were
reported, the elevation uncertainty is large (
One study reported U-series ages from corals cored on Amédée Islet, New Caledonia (Frank et al., 2006; for regional review, see Hallmann et al., 2020). In total, 19 analyses were reported for 15 corals, with one coral dated five times. The study authors used open-system ages (Thompson et al., 2003; Villemant and Feuillet, 2003) to confirm the existence of an LIG reef deposit within the core records and estimated a subsidence rate of 0.16 m/kyr for the study site. The strict and flexible closed-system criteria rejected all of the ages from New Caledonia.
A single coral with a late MIS 6 age (KE12-001; 133.5
LIG fossil coral U-series ages are available from uplifted coral reef
terraces on the Huon Peninsula, Papua New Guinea
(Cutler
et al., 2003; Esat et al., 1999; Stein et al., 1993; for a regional overview,
see Hallmann et al., 2020). The region has experienced substantial uplift
since the LIG, with local uplift rates estimated to be
Corals CU03-011, CU03-023 and ES99-020 do not have any contextual
information that can be used to determine if they are in primary growth
position, so we did not treat these samples as RSL indicators. ST93-005,
ST93-006, ST93-007 and ST93-009 are in primary growth position, but there
are no published paleowater depth interpretations provided. Additionally,
there are insufficient modern observations for
One study published coral U-series ages for emergent coral reef terraces
along the Red Sea coast of Saudi Arabia
(Manaa et al., 2016). In total, study
authors reported U-series ages for 25 coral samples and accepted 17 of the
ages. Using the strict closed-system screening criteria, that number is
reduced to three samples collected from reef terraces near the port city of
Yanbu. Two of the samples (MA16-009 and MA16-010) were collected from the
lower Yanbu terrace and yielded ages of 42.2
Two studies from the Seychelles published U-series coral ages
(Dutton et al., 2015b;
Israelson and Wohlfarth, 1999; for a regional overview, see Boyden et al.,
2021), containing a total of 67 U-series measurements for 31 individual
coral specimens. Approximately half (15) of the corals were dated in
triplicate, with three corals measured in duplicate. In the original
studies, 24 of the corals yielded acceptable ages (38 unique U-series ages).
Under the strict screening protocol, only five unique U-series ages from
three corals are accepted. This is increased to 25 U-series ages from 14
corals once the flexible screening criteria are applied, with ages ranging
from a weighted mean age of 122.2
Multiple sources have interpreted the Seychelles deposits as having formed
in an intertidal to upper subtidal zone, which, based on modern analogues
from these same islands, results in a maximum water depth of 2 m
(Dutton et al.,
2015b; Israelson and Wohlfarth, 1999; Montaggioni and Hoang, 1988). Here,
the maximum paleowater depth of 2 m was adopted, with one exception. Sample
IS99-010, a
LIG coral ages were reported for subtidal deposits on the Yorke Peninsula
near Adelaide, South Australia (Pan et al., 2018). Four
U-series ages were reported by the authors from four unique specimens of the
solitary coral
In the US Virgin Islands, sediment cores from Holocene reefs off the island
of St. Croix possess LIG reef deposits in the underlying substrate
(Toscano et al., 2012). St.
Croix is unique among many other Caribbean LIG sites in that all but
one of the LIG fossil reef localities are presently submerged below modern
sea level, and there is an apparent 0.62 m/km gradient between LIG deposits
from the northwestern and northeastern ends of the island. The authors
interpreted this gradient as having resulted from differential subsidence or
tilting caused by regional tectonism
(Toscano et al., 2012, and
references therein). Six corals from this study yielded LIG ages, five from
drill cores on Tague Reef on the northeastern end of St. Croix and one from
a drill core farther west, on Long Reef. Toscano et al. (2012) accepted all
ages except the one from Long Reef (TO12-010). The strict closed-system
criteria yielded similar results, but we rejected coral TO12-008 from
Tague Reef because of an elevated
In Toscano et al. (2012), corals that were not in primary growth position
were listed as “fragments”. Since none of the corals that passed
geochemical screening were stated as being fragments in the
Toscano et al. (2012)
supplement, we have treated them as being in primary growth position. The
authors interpreted the Tague Reef LIG deposit as being part of a reef
flat/back-reef setting in
U-series ages have been reported for 19 corals collected from the LIG Boat Cove and South Reef units on West Caicos (Kindler and Meyer, 2012; Kerans et al., 2019). Additional mass spectrometric U-series ages have been reported by Simo et al. (2008), but the type of material dated ranged from “well preserved coral, to skeletal grains and ooids”. As Simo et al. (2008) did not specify which carbonate material was dated for each of their ages, their dataset was not included in the present compilation.
Of all the ages reported, a total of 13 were accepted by the study authors. Under both the strict and flexible screening criteria, the two ages from Kindler and Meyer (2012) were rejected due to high calcite content. For the Kerans et al. (2019) study, calcite content was not reported for each sample, but the authors stated that XRD measurements indicated “a range of calcitization 100 % calcite to 3 % calcite”, so the authors instead used Sr element mapping to identify the best-preserved sections of coral to date. Based on the range of calcite concentrations given, none of the samples would pass the strict/flexible protocols, so these samples were also rejected.
Edwards et al. (1987b)
reported LIG U-series ages for uplifted coral terraces on Efate Island,
Vanuatu. In total, there are three U-series ages for two corals, with one
coral (ED87-010) measured in duplicate. All three ages were accepted by the
study authors and also passed the strict and flexible closed-system
criteria. ED87-010 has a weighted mean age of 130.6
Fossil corals from the coastline of Western Australia represent perhaps the broadest geographic region reported here, spanning more than 1400 km from Cape Range in the north to Foul Bay near the southwestern tip of the Australian continent. It has one of the largest number of U-series ages of any study area covered by WALIS, with 176 U-series ages reported for 156 unique coral specimens (Collins et al., 2003; Eisenhauer et al., 1996; Hearty et al., 2007; O'Leary et al., 2008a, b, 2013; McCulloch and Mortimer, 2008; Stirling et al., 1995, 1998). These sites are considered to be tectonically stable, with one notable exception being sites near the Cape Cuvier anticline, for which there is strong evidence of neotectonism since the LIG (Whitney and Hengesh, 2015).
In the original studies, at least 59 of the U-series ages from 55 coral were
accepted. Under the strict screening protocol, the total number of accepted
ages dropped substantially to just nine, from five corals, largely because
calcite content was not reported in many of the studies. This resulted in 75 % of the dataset being summarily rejected without any assessment of age
quality. To remedy this, for the flexible screening protocol, we allowed
samples without reported calcite content to be screened using
Of the samples that passed the flexible screening protocol, 42 were in
primary growth position (45 analyses total) and can be used as RSL
indicators. Explicit paleowater depth interpretations were not provided in
most cases, so we assigned the modern coral depth distributions for the
relevant taxa (OBIS, 2014). It should be noted, however, that many of the
samples in the dataset were collected from the very top of the LIG reef
outcrops and were likely growing within a few meters of sea level. For
samples from Shark Bay (OL08-002, OL08-003, OL08-009, OL08-010), no coral
taxonomic information was provided, so these samples should be treated as
marine limiting. Additionally, two samples from the Houtman Abrolhos islands
(ZH93-001, ZH93-005) were interpreted as being intertidal or subtidal deposits
and can be constrained to
Fossil coral U-series ages were reported for emergent reef terraces in Yemen, along the Al-Hajaja coast and on Perim Island (Al-Mikhlafi et al., 2018). In total, 35 U-series ages were reported for 33 coral specimens, with two corals dated in duplicate. Al-Mikhlafi et al. (2018) concluded that terrace Tr3 from the study area was LIG in age but decided against using any of the samples collected as RSL indicators, as most of the corals were diagenetically altered. None of the U-series ages from Yemen met the strict or flexible closed-system criteria.
Two reef tracts were uncovered during the excavation and construction of the
Xcaret theme park near Playa del Carmen, Mexico (see Simms, 2021, for a regional
overview). U-series ages are available from both reef tracts, which included
Multiple studies published coral U-series ages
Holocene coral U-series ages are not included in this study. These data are,
however, being compiled by the HOLSEA working group
(Khan et al., 2019;
One of the outstanding controversies for fossil coral RSL reconstructions is whether fossil reef sites record evidence of millennial- or centennial-scale sea-level change within the LIG. Constraining the anatomy (pattern) of GMSL change within the LIG is crucial for our understanding of ice sheet dynamics in warm interglacial periods, such as today, and has direct bearing on future projections of sea-level response to anthropogenic forcing (Church et al., 2013; DeConto and Pollard, 2016; Sweet et al., 2017). The analytical precision of U-series dating and field surveying techniques has advanced dramatically over the past 30 years, but this key question remains unresolved (Kopp et al., 2017).
The current version of the dataset can be accessed using the following link:
Reconciling different interpretations of GMSL pathways during the LIG will
require an approach that integrates age, elevation and sedimentary/facies
evidence at key fossil reef sites. At the site/regional level, precise
U-series age constraints are needed for key LIG fossil reef sites and must
be combined with a rigorous assessment of diagenesis and its effect on
U-series age quality
(Dechnik
et al., 2017; Dutton et al., 2015b; Obert et al., 2016; Tomiak et al.,
2016). Our understanding of LIG sea-level change will be further advanced if
efforts are made to better integrate U-series age information within the
context of coral elevation and existing site metadata (e.g., facies analysis,
paleoecological interpretations). Moving forward, there are several “best practices”
that can further this goal, including the following:
During field collection, the vertical position and depositional context
should be thoroughly documented, including an assessment of whether the
sampled coral is in primary growth position. Whenever possible, multiple subsamples of an LIG fossil coral should
be dated to screen for open-system behavior and verify age reproducibility. Finally, U-series ages that are accepted should be evaluated in the context
of existing facies and paleoecological interpretations for the study site,
to quantify the paleowater depth uncertainty for each fossil coral RSL data
point.
These interpretations are needed to ensure that U-series-dated fossil corals
continue to provide robust RSL information that can answer important
questions about LIG sea level.
The supplement related to this article is available online at:
PMC compiled the coral U-series database, developed the closed-system screening protocols and wrote the paper with assistance and guidance from AD. PMC and AD designed the U-series database structure.
The authors declare that they have no conflict of interest.
Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
This article is part of the special issue “WALIS – the World Atlas of Last Interglacial Shorelines”. It is not associated with a conference.
This database was compiled in WALIS, a sea-level database interface developed by the ERC Starting Grant “WARMCOASTS” (ERC-StG-802414), in collaboration with the PALSEA (PAGES/INQUA) working group. The database structure was designed by Alessio Rovere, Deirdre Ryan, Thomas Lorscheid, Andrea Dutton, Peter Chutcharavan, Dominik Brill, Nathan Jankowski, Daniela Mueller, Melanie Bartz, Evan Gowan and Kim Cohen. We thank Barbara Mauz as well as two anonymous referees for the helpful feedback they provided during the open discussion period, as well as Alessio Rovere for his assistance in designing and implementing the U-series and fossil coral RSL components of the WALIS interface and Karla Rubio Sandoval who helped compile data for the portions of the Curaçao fossil reef sites.
This research has been supported by the National Science Foundation (grant nos. 1702740 and 1443037).
This paper was edited by Alessio Rovere and reviewed by two anonymous referees.