Compilation of Last Interglacial (Marine Isotope Stage 5e) sea level indicators in the Bahamas, Turks and Caicos, and the east coast of Florida, USA

This paper provides a summary of published sea level archives representing the past position of sea level during the Last Interglacial sea level highstand in the Bahamas, Turks and Caicos, and the eastern (Atlantic) coast of Florida, USA. These data were assembled as part of a community effort to build the World Atlas of Last Interglacial Shorelines (WALIS) database. Shallow marine deposits from this sea level highstand are widespread across the region and are dominated by carbonate sedimentary features. In addition to depositional (constructional) sedimentary indicators of past sea level position, there is also evidence of erosion, dissolution, and/or subaerial exposure in places that can place an upper limit on the position of sea level. The sea level indicators that have been observed within this region and attributed to Marine Isotope Stage (MIS) 5e include corals, oolites, and other coastal sedimentary features. Here we compile a total of 50 relative sea level indicators including 36 in the Bahamas, three in West Caicos, and a remaining 10 for the eastern seaboard of Florida. We have also compiled U-Th age data for 24 fossil corals and 56 oolite samples. While some of these archives have been dated using U-Th disequilibrium methods, amino acid racemization, or optically stimulated luminescence, other features have more uncertain ages that have been deduced in the context of regional mapping and stratigraphy. Sedimentary archives in this region that constrain the elevation of the past position of sea level are associated with uncertainties that range from a couple decimeters to several meters. Across the Bahamas and on West Caicos, one of the observations that emerges from this compilation is that estimation of sea level position in this region during Marine Isotope Stage 5e is complicated by widespread stratigraphic evidence for at least one sea level oscillation. This evidence is defined by submarine features separated by erosion and subaerial exposure, meaning that there were likely multiple distinct peaks in sea level rather than just one. To this end, the timing of these individual sea level indicators becomes important when compiling and comparing data across the region given that different archives may have formed during different sub-orbital peaks in sea level.

Modern and sub-fossil corals suggest reduced temperature variability in the eastern pole of the Indian Ocean Dipole during the medieval climate anomaly

We present two 40 year records of monthly coral Sr/Ca ratios from the eastern pole of the Indian Ocean Dipole. A modern coral covers the period from 1968 to 2007. A sub-fossil coral derives from the medieval climate anomaly (MCA) and spans 1100–1140 ad. The modern coral records SST variability in the eastern pole of the Indian Ocean Dipole. A strong correlation is also found between coral Sr/Ca and the IOD index. The correlation with ENSO is asymmetric: the coral shows a moderate correlation with El Niño and a weak correlation with La Niña. The modern coral shows large interannual variability. Extreme IOD events cause cooling > 3 °C (1994, 1997) or ~ 2 °C (2006). In total, the modern coral indicates 32 warm/cool events, with 16 cool and 16 warm events. The MCA coral shows 24 warm/cool events, with 14 cool and 10 warm events. Only one cool event could be comparable to the positive Indian Ocean Dipole in 2006. The seasonal cycle of the MCA coral is reduced (< 50% of to the modern) and the skewness of the Sr/Ca data is lower. This suggests a deeper thermocline in the eastern Indian Ocean associated with a La Niña-like mean state in the Indo-Pacific during the MCA.

Fossil Corals With Various Degrees of Preservation Can Retain Information About Biomineralization-Related Organic Material

Scleractinian corals typically form a robust calcium carbonate skeleton beneath their living tissue. This skeleton, through its trace element composition and isotope ratios, may record environmental conditions of water surrounding the coral animal. While bulk unrecrystallized aragonite coral skeletons can be used to reconstruct past ocean conditions, corals that have undergone significant diagenesis have altered geochemical signatures and are typically assumed to retain insufficient meaningful information for bulk or macrostructural analysis. However, partially recrystallized skeletons may retain organic molecular components of the skeletal organic matrix (SOM), which is secreted by the animal and directs aspects of the biomineralization process. Some SOM proteins can be retained in fossil corals and can potentially provide past oceanographic, ecological, and indirect genetic information. Here, we describe a dataset of scleractinian coral skeletons, aged from modern to Cretaceous plus a Carboniferous rugosan, characterized for their crystallography, trace element composition, and amino acid compositions. We show that some specimens that are partially recrystallized to calcite yield potentially useful biochemical information whereas complete recrystalization or silicification leads to significant alteration or loss of the SOM fraction. Our analysis is informative to biochemical-paleoceanographers as it suggests that previously discounted partially recrystallized coral skeletons may indeed still be useful at the microstructural level.

The Distribution Coefficients of Major and Minor Elements in Coral Skeletons Under Variable Calcium Seawater Concentrations

Coral skeletons are one of the best archives for past ocean seawater (SW) chemistry and isotopes. However, the distribution coefficients of major and minor elements in coral skeletons are not well determined. In this study, we launched an experiment to determine the distribution coefficients of multiple elements in corals’ skeletons by changing Ca concentrations in SW (CaSW). Two scleractinian corals, Pocillopora damicornis and Acropora cervicornis were cultured in modified Gulf of Eilat water (Red-Sea) with CaSW of approximately 10, 15, 20, and 25 mM. After almost three months, the newly grown skeletons were analyzed for the following elements: Li, Na, Mg, K, Sr, and Ba. Their ratios to Ca in the coral skeleton (El/Cacoral) increased linearly with El/CaSW (with R2 values above 0.98), crossing the origin and thus indicating constant distribution coefficient for each element over the experimental range of El/CaSW. The values of DEl were in good agreement with values reported for corals collected in natural seawater. However, differences were observed between the two species, and both were slightly deviating from inorganic aragonite D values. These deviations are well explained by Rayleigh fractionation process in the calcifying fluid (assuming it is mainly seawater). This was observed both for elements with D &gt; 1 (Ba and Sr) and D &lt; 1 (Li, Mg, Na, and K). P. damicornis showed open system behavior (∼20% of its Ca utilized) while A. cervicornis showed more closed calcifying reservoir (∼50% of its Ca utilized). The finding that the distribution coefficients of the six minor and trace elements are constant for a given species, should help in the reconstruction of past seawater chemistry based on multielement measurements in fossil corals. In particular, Na/Cacoral can be used to reconstruct past ocean Ca concentrations and with El/Cacoral ratios for other elements, their concentrations for the Cenozoic can be reconstructed.

Living evidence of a fossil survival strategy raises hope for warming-affected corals

Climate change is affecting reef-building corals worldwide, with little hope for recovery. However, coral fossils hint at the existence of environmental stress–triggered survival strategies unreported in extant colonial corals. We document the living evidence and long-term ecological role of such a survival strategy in which isolated polyps from coral colonies affected by warming adopt a transitory resistance phase, in turn expressing a high recovery capacity in dead colony areas. Such processes have been described in fossil corals as rejuvenescence but were previously unknown in extant reef-builder corals. Our results based on 16 years of monitoring show the significance of this process for unexpected recoveries of coral colonies severely affected by warming. These findings provide a link between rejuvenescence in fossil and extant corals and reveal that beyond adaptation and acclimatization processes, modern scleractinian corals show yet undiscovered and highly effective survival strategies that help them withstand and recover from rapid environmental changes.

CLOSING THE IRON CURTAIN: HOW GEOLOGISTS IN BERLIN EXPERIENCED THE COLD WAR ERA

ABSTRACT After World War II, the geological community in Germany was severely disrupted. Nevertheless, there were also first attempts to mend severed professional ties by contacting colleagues within Germany and outside. As far as logistically possible under the difficult circumstances of the time, publications and maps, paleontological specimens and geological information were exchanged, e.g., between East-Berlin (Soviet Sector of the divided city) and Hannover (within the British Occupation Area) or Tübingen (within the French Occupation Area), and vice versa. Over the next couple of years, however, matters of logistics did not become easier—to the contrary. Berlin colleagues reported increasing political pressure and many left eastern Germany to seek employment in the west. Those that remained were forced to abandon professional bonds with the western zones. Whereas it seemed comparatively harmless, when one had sent a few fossil corals from Berlin on loan to Tübingen, those that had sent information on petroleum and ore deposits suddenly found themselves charged with espionage and high treason, facing imprisonment and potentially worse. As a consequence, letters crossing the border became less and less frequent and geologists like everybody else settled into two different worlds separated by the ‘Iron Curtain’.