Geology topics

Jennifer A. Flannery

Publications and source records attributed to Jennifer A. Flannery.

13 recordsLinked to original sources

USGS2025

Snapshots of mid-to-late Holocene sea-surface temperature variability from a subtropical western Atlantic coral reef

Large-scale Holocene climate reconstructions rely heavily on extratropical proxy records. Coral-based temperature reconstructions from the tropical and subtropical oceans therefore fill a critical spatial and temporal data gap, allowing for reconstruction of seasonally resolved temperature variability. We present five new, monthly-resolved sea-surface temperature (SST) reconstructions (between 39 and 57 years in length) from 2 to 7 thousand years ago (ka) based on the strontium-to‑calcium ratio (Sr/Ca) of Orbicella faveolata corals from subtropical reefs in south Florida. Modern calibrations between O. faveolata Sr/Ca and in situ SST from the region allow us to directly compare the mean and variability of SSTs since the mid-Holocene. In contrast to the low climate variability observed in more tropical areas of the western Atlantic during the Holocene, our records from subtropical south Florida exhibit pronounced changes in mean SST and variability. Our records suggest that mid-Holocene SSTs in the Florida Keys were highly variable, with relatively cooler winters driving a cooler mean SST at ∼6.7 ka (23.7 ± 0.6°C at 6.7 ka and 25.0 ± 0.5°C at 6.6 ka), and relatively warmer summers and more variable temperatures by 5.8 ka (27.1 ± 0.4°C, seasonality of 8.7°C). We also analyzed stable oxygen isotopes in two of our corals and those data support our Sr/Ca-based estimate of climatic warming between 6.6 ka and 5.8 ka (−3.6‰ and − 3.9‰). Both winter and summer temperatures were significantly cooler than the other mid-to-late Holocene snapshots at 3.6 ka (21.2 ± 0.5°C) and SST warmed but remained highly variable at 2.6 ka (25.0 ± 0.6°C, seasonality of 7.9°C). These centennial-scale changes in climate variability potentially contributed to the regional shutdown of reef accretion by the late Holocene. Our reconstructions provide a proof-of-concept study that highlights the value of coral-based SST records from highly sensitive, subtropical locations for understanding Holocene climate on seasonal to centennial timescales.

Florida↗

USGS2024

20th century warming in the lower Florida Keys was dominated by increasing winter temperatures

Long-lived Atlantic coral species like Orbicella faveolata are important archives of oceanographic change in shallow, marine environments like the Florida Keys. Not only can coral-based records extend for multiple centuries beyond the limits of the instrumental record, but they can also provide a more accurate representation of in situ conditions than gridded interpolated sea-surface temperature (SST) products for nearshore reef environments. We use the coral Sr/Ca paleothermometer to produce a 150-year (1830–1980 C.E.) monthly SST reconstruction from an O . faveolata colony collected in the Marquesas Keys, FL, USA. An important feature of our record is a significant 20th-century warming trend in winter SSTs. We hypothesize that the winter warming trend was driven partially by a decrease in upwelling associated cyclonic eddies spinning off the Florida Current. A long-term weakening of winter Florida Current transport over the 20th century could be responsible for decreased cyclonic eddy formation in the Florida Straits. Another feature of the record is pronounced multidecadal fluctuations of mean annual warming and cooling in the record, which correspond to Atlantic Multidecadal Variability (AMV), with the AMV lagging behind western Florida Keys temperatures by 5–11 years. Strong coherence between coral-based SST reconstructions in the western Florida Keys with broader scale Atlantic oceanographic trends over the past century suggests a common driver of regional SST variability.

Florida↗

USGS2020

Imprint of regional oceanography on foraminifera of eastern Pacific Coral Reefs

The marginal marine environments of the eastern tropical Pacific (ETP) serve as an ideal natural laboratory to study how oceanographic and climatic variability influence coral-reef ecosystems. Reefs along the Pacific coast of Panamá span a natural gradient of nutrients, pH, and temperature as a result of stronger seasonal upwelling in the Gulf of Panamá relative to the Gulf of Chiriquí. The ecosystems are not only influenced by spatial and seasonal variations in oceanography but are affected by the climatic variability of the El Niño-Southern Oscillation (ENSO). Foraminifera can be robust indicators of ecosystem condition because the composition of their assemblages and the geochemistry of their tests can change rapidly in response to environmental variability. We studied benthic foraminifera in sediment samples collected from 3 m below mean sea level in the Gulf of Panamá and the Gulf of Chiriquí. Temperature loggers deployed from 2016 to 2019 showed that average temperatures were lower and more variable in the Gulf of Panamá due to seasonal upwelling. All sites in both gulfs were dominated by heterotrophic foraminifera, which was likely the result of nutrient enrichment due to upwelling, combined with ENSO effects. However, the Gulf of Chiriquí was characterized by higher abundances of symbiont-bearing foraminifera than the Gulf of Panamá. The orders Miliolida and Rotaliida dominated the foraminiferal assemblages in both gulfs, with Quinqueloculina and Rosalina being the most abundant genera in the two orders, respectively. Miliolids were less abundant in the Gulf of Panamá than in the Gulf of Chiriquí, whereas rotaliid densities were not significantly different between the two gulfs. Lower pH in the Gulf of Panamá as a result of upwelling may have contributed to the lower abundance of miliolids, which secrete tests of high-magnesium calcite. Geochemical analysis of tests of the symbiont-bearing miliolid Sorites marginalis revealed that foraminiferal Mg/Ca ratios were lower in the Gulf of Panamá than in the Gulf of Chiriquí. The offset in foraminiferal Mg/Ca is consistent with the lower mean annual temperature observed in the Gulf of Panamá due to stronger seasonal upwelling. Because the geochemistry and assemblages of foraminifera reflect differences in environmental conditions, they could potentially be used in tandem with coral proxies to reconstruct past environmental change and project the future of coral-reef systems within the ETP.

Gulf of Chiriqui, Gulf of Panama↗

USGS2019

Characterization of the exoskeleton of the Antarctic king crab Paralomis birsteini

Ocean acidification is projected to inhibit the biogenic production of calcium-carbonate skeletons in marine organisms. Antarctic waters represent a natural environment in which to examine the long-term effects of carbonate undersaturation on calcification in marine predators. King crabs (Decapoda: Anomura: Lithodidae), which currently inhabit the undersaturated environment of the continental slope off Antarctica, are potential invasives on the Antarctic shelf as oceanic temperatures rise. Here, we describe the chemical, physical, and mechanical properties of the exoskeleton of the deep-water Antarctic lithodid Paralomis birsteini and compare our measurements with two decapod species from shallow water at lower latitudes: Cancer borealis (Brachyura: Cancridae) and Callinectes sapidus (Brachyura: Portunidae). Paralomis birsteini deposit proportionally more calcium carbonate in their predatory chelae than their protective carapaces, compared with the other two crab species. When exoskeleton thickness and microhardness were compared between the chelae and carapace, the magnitude of the difference between these body regions was significantly greater in P. birsteini than in the other species tested. Hence, there appeared to be a greater disparity in P. birsteini in overall investment in calcium-carbonate structures among regions of the exoskeleton. The imperatives of prey consumption and predator avoidance may be influencing the deposition of calcium to different parts of the exoskeleton in lithodids living in an environment undersaturated with respect to calcium carbonate.

Invertebrate Biology↗

USGS2018

Quantifying uncertainty in Sr/Ca-based estimates of SST from the coral Orbicella faveolata

The strontium to calcium ratio (Sr/Ca) in aragonitic skeletons of massive corals provides a proxy for sea surface temperature (SST) that can be used to reconstruct paleoclimates across decades, centuries, and, potentially, millennia. Determining the reproducibility of Sr/Ca records among contemporaneous coral colonies from the same region is critical to quantifying uncertainties associated with the Sr/Ca‐SST proxy. We evaluated both intracolony and intercolony variability in Sr/Ca using five modern colonies of Orbicella faveolata collected live from the Dry Tortugas National Park, FL. We regressed all available Sr/Ca‐SST data pairs from the five O. faveolata colonies against the Advanced Very High Resolution Radiometer gridded SST data set to produce a new Sr/Ca‐SST calibration equation (Sr/Ca = −0.049 × SST + 10.460), which we suggest can be applied to O. faveolata colonies collected throughout the Gulf of Mexico/Caribbean region. We estimated total uncertainty by calculating the root‐mean‐square of the intracolony, intercolony, and analytical error terms. Our (1σ) uncertainty estimates of 0.082 mmol/mol (1.66 °C) for subannual Sr/Ca‐SST and 0.070 mmol/mol (1.43 °C) for mean annual Sr/Ca‐SST represent conservative error terms that can be applied to individual data points in single‐colony Sr/Ca‐SST reconstructions. We illustrate how these uncertainties can be significantly reduced by generating multicolony reconstructions and/or through replication of sampling within individual coral colonies. Although the uncertainties on absolute Sr/Ca‐based SST are likely too large to allow researchers to evaluate subdecadal temperature variability, we show that the O. faveolata paleothermometer can reliably detect changes of ~2 °C across decadal timescales and ~1 °C over multidecadal timescales.

Paleoceanography and Paleoclimatology↗

USGS2017

Multi-species coral Sr/Ca-based sea-surface temperature reconstruction using Orbicella faveolata and Siderastrea siderea from the Florida Straits

We present new, monthly-resolved Sr/Ca-based sea-surface temperature (SST) records from two species of massive coral, Orbicella faveolata and Siderastrea siderea, from the Dry Tortugas National Park, FL, USA (DTNP). We combine these new records with published data from three additional S. siderea coral colonies to generate a 278-year long multi-species stacked Sr/Ca-SST record from DTNP. The composite record of mean annual Sr/Ca-SST at DTNP shows pronounced decadal-scale variability with a range of 1 to 2°C. Notable cool intervals in the Sr/Ca-derived SST lasting about a decade centered at ~1845, ~1935, and ~1965 are associated with reduced summer Sr/Ca-SST (monthly maxima < 29°C), and imply a reduction in the spatial extent of the Atlantic Warm Pool (AWP). There is significant coherence between the composite DTNP Sr/Ca-SST record and the Atlantic Multidecadal Oscillation (AMO) index, with the AMO lagging Sr/Ca-SST at DTNP by 9 years. Low frequency variability in the Gulf Stream surface transport, which originates near DTNP, may provide a link for the lagged relationship between multidecadal variability at DTNP and the AMO.

Florida↗

USGS2016

A methodology for quantifying trace elements in the exoskeletons of Florida stone crab ( Menippe mercenaria ) larvae using inductively coupled plasma optical emission spectrometry (ICP–OES)

The larvae of the Florida stone crab, Menippe mercenaria , migrate through a variety of habitats as they develop and, therefore, experience a broad range of environmental conditions through ontogeny. Environmental variability experienced by the larvae may result in distinct elemental signatures within the exoskeletons, which could provide a tool for tracking the environmental history of larval stone crab populations. A method was developed to examine trace-element ratios, specifically magnesium-to-calcium (Mg/Ca) and strontium-to-calcium (Sr/Ca) ratios, in the exoskeletons of M. mercenaria larvae. Two developmental stages of stone crab larvae were analyzed—stage III and stage V. Specimens were reared in a laboratory environment under stable conditions to quantify the average ratios of Mg/Ca and Sr/Ca of larval stone crab exoskeletons and to determine if the ratios differed through ontogeny. The elemental compositions (Ca, Mg, and Sr) in samples of stage III larvae (n = 50 per sample) from 11 different broods (mean Sr/Ca = 5.916 ± 0.161 millimole per mole [mmol mol −1 ]; mean Mg/Ca = 218.275 ± 59.957 mmol mol −1 ) and stage V larvae (n = 10 per sample) from 12 different broods (mean Sr/Ca = 6.110 ± 0.300 mmol mol −1 ; mean Mg/Ca = 267.081 ± 67.211 mmol mol –1 ) were measured using inductively coupled plasma optical emission spectrometry (ICP–OES). The ratio of Sr/Ca significantly increased from stage III to stage V larvae, suggesting an ontogenic shift in Sr/Ca ratios between larval stages. The ratio of Mg/Ca did not change significantly between larval stages, but variability among broods was high. The method used to examine the trace-element ratios provided robust, highly reproducible estimates of Sr/Ca and Mg/Ca ratios in the larvae of M. mercenaria , demonstrating that ICP–OES can be used to determine the trace-element composition of chitinous organisms like the Florida stone crab.

Open-File Report↗

USGS2015

The relationship between the ratio of strontium to calcium and sea-surface temperature in a modern Porites astreoides coral: Implications for using P. astreoides as a paleoclimate archive

An inverse relationship has been demonstrated between water temperature and the ratio of strontium to calcium (Sr/Ca) in coral aragonite for a number of Pacific species of the genus Porites . This empirically determined relationship has been used to reconstruct past sea-surface temperature (SST) from modern and Holocene age coral archives. A study was conducted to investigate this relationship for Porites astreoides to determine the potential for using these corals as a paleotemperature archive in the Caribbean and western tropical Atlantic Ocean. Skeletal aragonite from a P. astreoides colony growing offshore of the southeast coast of Florida was subsampled with a mean temporal resolution of 14 samples per year and analyzed for Sr/Ca. The resulting Sr/Ca time series yielded well-defined annual cycles that correspond to annual growth bands in the coral. Sr/Ca was regressed against a monthly SST record from C-MAN buoy station FWYF1 (located at Fowey Rocks, Florida), resulting in the following Sr/Ca-SST relationship: Sr/Ca = –0.040*SST + 10.128 (R = –0.77). A 10-year time series of Sr/Ca-derived SST yields annual cycles with a 10–12 degree Celsius seasonal amplitude, consistent with available local instrumental records. We conclude that Sr/Ca in Porites astreoides from the Caribbean/Atlantic region has high potential for developing subannually resolved modern and recent Holocene SST records.

Florida↗

USGS2014

A reconstruction of sea surface temperature variability in the southeastern Gulf of Mexico from 1734 to 2008 C.E. using cross-dated Sr/Ca records from the coral Siderastrea siderea

This study uses skeletal variations in coral Sr/Ca from three Siderastrea siderea coral colonies within the Dry Tortugas National Park in the southeastern Gulf of Mexico (24°42′N, 82°48′W) to reconstruct monthly sea surface temperature (SST) variations from 1734 to 2008 Common Era (C.E.). Calibration and verification of the replicated coral Sr/Ca-SST reconstruction with local, regional, and historical temperature records reveals that this proxy-temperature relationship is stable back to 1879 C.E. The coral SST reconstruction contains robust interannual (~2.0°C) and multidecadal variability (~1.5°C) for the past 274 years, the latter of which does not covary with the Atlantic Multidecadal Oscillation. Winter SST extremes are more variable than summer SST extremes (±2.2°C versus ±1.6°C, 2 σ ) suggesting that Loop Current transport in the winter dominates variability on interannual and longer time scales. Summer SST maxima are increasing (+1.0°C for 274 years, σ MC = ±0.5°C, 2 σ ), whereas winter SST minima contain no significant trend. Colder decades (~1.5°C) during the Little Ice Age (LIA) do not coincide with decades of sunspot minima. The coral SST reconstruction contains similar variability to temperature reconstructions from the northern Gulf of Mexico (planktic foraminifer Mg/Ca) and the Caribbean Sea (coral Sr/Ca) suggesting areal reductions in the Western Hemisphere Warm Pool during the LIA. Mean summer coral SST extremes post-1985 C.E. (29.9°C) exceeds the long-term summer average (29.2°C for 1734–2008 C.E.), yet the warming trend after 1985 C.E. (0.04°C for 24 years, σ MC = ±0.5, 2 σ ) is not significant, whereas Caribbean coral Sr/Ca studies contain a warming trend for this interval.

Florida↗

USGS2013

Sr/Ca proxy sea-surface temperature reconstructions from modern and holocene Montastraea faveolata specimens from the Dry Tortugas National Park

Sr/Ca ratios from skeletal samples from two Montastraea faveolata corals (one modern, one Holocene, ~6 Ka) from the Dry Tortugas National Park were measured as a proxy for sea-surface temperature (SST). We sampled coral specimens with a computer-driven triaxial micromilling machine, which yielded an average of 15 homogenous samples per annual growth increment. We regressed Sr/Ca values from resulting powdered samples against a local SST record to obtain a calibration equation of Sr/Ca = -0.0392 SST + 10.205, R = -0.97. The resulting calibration was used to generate a 47-year modern (1961-2008) and a 7-year Holocene (~6 Ka) Sr/Ca subannually resolved proxy record of SST. The modern M. faveolata yields well-defined annual Sr/Ca cycles ranging in amplitude from ~0.3 and 0.5 mmol/mol. The amplitude of ~0.3 to 0.5 mmol/mol equates to a 10-15°C seasonal SST amplitude, which is consistent with available local instrumental records. Summer maxima proxy SSTs calculated from the modern coral Sr/ Ca tend to be fairly stable: most SST maxima from 1961–2008 are 29°C ± 1°C. In contrast, winter minimum SST calculated in the 47-year modern time-series are highly variable, with a cool interval in the early to mid-1970s. The Holocene (~6 Ka) Montastraea faveolata coral also yields distinct annual Sr/Ca cycles with amplitudes ranging from ~0.3 to 0.6 mmol/mol. Absolute Sr/Ca values and thus resulting SST estimates over the ~7-year long record are similar to those from the modern coral. We conclude that Sr/Ca from Montastraea faveolata has high potential for developing subannually resolved Holocene SST records.

Florida↗

USGS2013

Complexity of nearshore strontium-to-calcium ratio variability in a core sample of the massive coral Siderastrea siderea obtained in Coral Bay, St. John, U.S. Virgin Islands

Strontium-to-calcium ratios (Sr/Ca) were measured on the skeletal matrix of a core sample from a colony of the massive coral Siderastrea siderea collected in Coral Bay, St. John, U.S. Virgin Islands. Strontium and calcium are incorporated into the coral skeleton during the precipitation of aragonite by the coral polyps and their ratio is highly temperature dependent. The robustness of this temperature dependence makes Sr/Ca a reliable proxy for sea surface temperature (SST). Details presented from the St. John S. siderea core indicate that terrestrial inputs of sediment and freshwater can disrupt the chemical balance and subsequently complicate the utility of Sr/Ca in reconstructing historical SST. An approximately 44-year-long record of Sr/Ca shows that an annual SST signal is recorded but with an increasing Sr/Ca trend from 1980 to present, which is likely the result of runoff from the mountainous terrain of St. John. The overwhelming influence of the terrestrial fingerprint on local seawater chemistry makes utilizing Sr/Ca as a SST proxy in nearshore environments very difficult.

Open-File Report↗

USGS2013

Linear extension rates of massive corals from the Dry Tortugas National Park (DRTO), Florida

Colonies of three coral species, Montastraea faveolata , Diploria strigosa , and Siderastrea siderea , located in the Dry Tortugas National Park (DRTO), Florida, were sampled and analyzed to evaluate annual linear extension rates. Montastraea faveolata had the highest average linear extension and variability in (DRTO: C2 = 0.67 centimeters/year (cm yr -1 ) ± 0.04, B3 = 0.85 cm yr -1 ± 0.07), followed by D. strigosa (DRTO: C1 = 0.73 cm yr -1 ± 0.04; MK = 0.59 cm yr -1 ± 0.06) and S. siderea (DRTO: A1 = 0.41 cm yr -1 ± 0.03). Intercolony comparison of M. faveolata from DRTO yielded a significant correlation (r = 0.34, df = 67, P = 0.005) and similar long-term patterns. DRTO S. siderea core A1 showed an overall increasing trend (r = 0.61, df = 119, P < 0.0001) in extension rates that correlated significantly with International Comprehensive Ocean/Atmosphere Data Set annual sea-surface temperature (r = 0.42, df = 115, P < 0.0001) and an air temperature record from Key West (r = 0.37, df = 111, P < 0.0001). In conclusion, annual linear extension rates are species specific and potentially influence by long-term variability in sea-surface temperature.

Florida↗

USGS2010

Corals as climate recorders

The U.S. Geological Survey (USGS) Coral Reef Ecosystem Studies (CREST) Project is analyzing corals from various sites in the Caribbean region, Dry Tortugas National Park, Biscayne National Park, other areas of the Florida Keys, and the Virgin Islands. The objective of this project is to develop records of past environmental change to better our understanding of climate variability. The records are being used to document changes over the last few centuries and to determine how corals and coral reefs have responded to any changes.

Fact Sheet↗