Signals of resilience to ocean change: high thermal tolerance of early stage Antarctic sea urchins (Sterechinus neumayeri) reared under present-day and future pCO2 and temperature

We tested the hypothesis that development of the Antarctic urchin Sterechinus neumayeri under future ocean conditions of warming and acidification would incur physiological costs, reducing the tolerance of a secondary stressor. The aim of this study is twofold: (1) quantify current austral spring temperature and pH near sea urchin habitat at Cape Evans in McMurdo Sound, Antarctica and (2) spawn S. neumayeri in the laboratory and raise early developmental stages (EDSs) under ambient (-0.7 °C; 400 µatm pCO2) and future (+2.6 °C; 650 and 1,000 µatm pCO2) ocean conditions and expose four EDSs (blastula, gastrula, prism, and 4-arm echinopluteus) to a one hour acute heat stress and assess survivorship. Results of field data from 2011 to 2012 show extremely stable inter-annual pH conditions ranging from 7.99 to 8.08, suggesting that future ocean acidification will drastically alter the pH-seascape for S. neumayeri. In the laboratory, S. neumayeri EDSs appear to be tolerant of temperatures and pCO2 levels above their current habitat conditions. EDSs survived acute heat exposures >20 °C above habitat temperatures of -1.9 °C. No pCO2 effect was observed for EDSs reared at -0.7 °C. When reared at +2.6 °C, small but significant pCO2 effects were observed at the blastula and prism stage, suggesting that multiple stressors are more detrimental than single stressors. While surprisingly tolerant overall, blastulae were the most sensitive stage to ocean warming and acidification. We conclude that S. neumayeri may be unexpectedly physiologically tolerant of future ocean conditions.

Tab. 1+2: C14-dates cf the older and younger emergence periods

In the neighbourhood of Oobloyah Bay various phenomena ean be eneountered whieh point to a ularge-seale uplift of shorelines, i.e. to an emergence of 200 m. Delta terraces, deltaic fan terraces and glacio-marine sands are regarded by the author as being the most reliable evidence of this. The marine limit documented by glacio-marine sand is to be found at ~170 m a.s.l. Hints of ancient shorelines located at a higher level exist only in the shape of badly preserved raised beaches. They were classified as less reliable records of past sea-levels, due to the lack of marine fossils and/or drift wood, and furthermore because those forms had been strongly influenced by periglacial processes. Deltaic deposits are of more importance in this context. The glacio-marine deltaic sands of several terrace levels contain terrestrial plant remnants which delivered C14dates. Using these dates und the relative elevations of terraces the emergenee of the area investigated could be recorded. This occured in a series of phases (and steps) which were summarized into two periods: an early period of emergenee which took place from at least 25 300 years B.P. to later than 17 340 years B.P. and a later one from at least 12 870 years B.P. up to the present day. The emergence seems to represent a discontinuous but regular sequence of relative sea level movements without intermittent submergence. Since the deltaic fans of the early emergence period were accumulated by sediments through glacio-fluvial channels of an adjacent glacier body the appropriate location of this glacial stage for one of the glaciers delivering meltwater (Nukapingwa Glacier) could be reconstructed. This stage of the glacier appears to belong to a retreating phase of the Mid-Wisconsin (?). The later period of emergence resulted in six rather glacio-marine delta terrace generations at the mouths of the main rivers with glaciofluvial regimen debouching into the Oobloyah Bay. A connection of this emergence with the glacial history of the field area is discussed. If one may rely on the age determinations of land derived plant fossils and their application for the climatic history of the area investigated, it must be concluded that the Heidelberg Valley, to a large extent, was alreaely deglaciated 25 000 years ago. The existence of a "Cockburn"-Phase in the sense of a major readvanee in Late Wisconsin times appears to be doubtful, or has been developed rather weakly.

Stable isotope and geochemical analyses of sediment core SO164-17-2 from the southern Florida Straits

Modeling and proxy studies indicate that a reduction of Atlantic Meridional Overturning Circulation (AMOC) strength profoundly impacts temperatures and salinities in the (sub)tropical Atlantic, especially on subsurface levels. While previous studies focused on prominent periods of AMOC reduction during the last deglaciation, we aim to test whether similar reconfigurations of the subtropical hydrography occurred during the moderate climatic alterations punctuating the last interglacial, Marine Isotope Stage (MIS) 5. Here, we present temperature and salinity records from a Florida Straits core by combining d18O and Mg/Ca analyses on surface (Globigerinoides ruber, white) and deep-dwelling (Globorotalia crassaformis) foraminifera, covering MIS 5 in high resolution. The data reveal increasing salinities at intermediate depths during interglacial cooling episodes, decoupled from relatively stable surface conditions. This probably indicates the spatial expansion of saline Subtropical Gyre waters due to enhanced Ekman downwelling and might also point to a changed density structure and altered geostrophic balance in Florida Straits. Notably, these oceanographic alterations are not consistently occurring during periods of AMOC reduction. The data suggest that the expansion of gyre waters into Florida Straits was impeded by the increasing influence of Antarctic Intermediate Water (AAIW) from MIS 5.5 to ~107 kyr BP. Afterwards, increasingly positive benthic d13C values imply a recession of AAIW, allowing the temporary expansion of Gyre waters into Florida Straits. We argue that the inferred transient subtropical salt accumulation and warm pool expansion might have played a pivotal role in reinvigorating meridional overturning and dampen the severity of interglacial cold phases.