Isotopic geochemistry of lavas at DSDP Holes 81-553 and 81-555

It is demonstrated by K-Ar analyses that the age of reversely magnetized basalts, which immediately predate magnetic Anomaly 24B, is 53.5 ± 1.9 m.y. Samples from deep levels appear to be grossly contaminated by an extraneous argon component with a uniform argon-40/argon-36 ratio 440. This component is thought to have been derived from fluids circulating in the lava pile during burial. The age result corroborates the assignment previously made to Anomaly 24B by Hailwood et al. (1979) and Lowrie and Alvarez (1981). It additionally suggests that lava extrusion formed part of a much larger magmatic event, which affected wide areas of the North Atlantic margins around the Paleocene/Eocene boundary, and can therefore probably be considered a good estimate of the age of this boundary. Initial 143Nd/144Nd ratios lie in the very restricted range 0.512920 ± 19 to 0.513026 ± 24 and initial 8 7Sr/86Sr ratios from ca. 0.703 to ca. 0.705. Acid leaching reduces the latter range to 0.70264 ± 4 to 0.70384 ± 4, suggesting that the higher 87Sr/86Sr ratios resulted from interaction with seawater. The array of data for treated samples is closely conformable on a 143Nd/144Nd-87Sr/86Sr diagram with the main oceanic mantle array and with previously published fields for Atlantic Ocean basalts. No evidence for any continental crustal contamination has been found. This suggests, but does not prove, that continental crust played no part in the genesis of these rocks.

Seawater carbonate chemistry and growth rate of Emiliania huxleyi in lab experiment

Predicting the impacts of environmental change on marine organisms, food webs, and biogeochemical cycles presently relies almost exclusively on short-term physiological studies, while the possibility of adaptive evolution is often ignored. Here, we assess adaptive evolution in the coccolithophore Emiliania huxleyi, a well-established model species in biological oceanography, in response to ocean acidification. We previously demonstrated that this globally important marine phytoplankton species adapts within 500 generations to elevated CO2. After 750 and 1000 generations, no further fitness increase occurred, and we observed phenotypic convergence between replicate populations. We then exposed adapted populations to two novel environments to investigate whether or not the underlying basis for high CO2-adaptation involves functional genetic divergence, assuming that different novel mutations become apparent via divergent pleiotropic effects. The novel environment "high light" did not reveal such genetic divergence whereas growth in a low-salinity environment revealed strong pleiotropic effects in high CO2 adapted populations, indicating divergent genetic bases for adaptation to high CO2. This suggests that pleiotropy plays an important role in adaptation of natural E. huxleyi populations to ocean acidification. Our study highlights the potential mutual benefits for oceanography and evolutionary biology of using ecologically important marine phytoplankton for microbial evolution experiments.

Sedimentary record of the western Amundsen Sea Embayment after the last glacial maximum

Reliable dating of glaciomarine sediments deposited on the Antarctic shelf since the Last Glacial Maximum (LGM) is very challenging because of the general absence of calcareous (micro-) fossils and the recycling of fossil organic matter. As a consequence, radiocarbon (14C) ages of the acid-insoluble organic fraction (AIO) of the sediments bear uncertainties that are very difficult to quantify. In this paper we present the results of three different chronostratigraphic methods to date a sedimentary unit consisting of diatomaceous ooze and diatomaceous mud that was deposited following the last deglaciation at five core sites on the inner shelf in the western Amundsen Sea (West Antarctica). In three cores conventional 14C dating of the AIO in bulk sediment samples yielded age reversals down-core, but at all sites the AIO 14C ages obtained from diatomaceous ooze within the diatom-rich unit yielded similar uncorrected 14C ages ranging from 13,517±56 to 11,543±47 years before present (yr BP). Correction of these ages by subtracting the core-top ages, which are assumed to reflect present-day deposition (as indicated by 21044 Pb dating of the sediment surface at one core site), yielded ages between ca. 10,500 and 8,400 calibrated years before present (cal yr BP). Correction of the AIO ages of the diatomaceous ooze by only subtracting the marine reservoir effect (MRE) of 1,300 years indicated deposition of the diatom-rich sediments between 14,100 and 11,900 cal yr BP. Most of these ages are consistent with age constraints between 13.0 and 8.0 ka BP for the diatom-rich unit, which we obtained by correlating the relative palaeomagnetic intensity (RPI) records of three of the sediment cores with global and regional reference curves for palaeomagnetic intensity. As a third dating technique we applied conventional 53 radiocarbon dating of the AIO included in acid-cleaned diatom hard parts that were extracted from the diatomaceous ooze. This method yielded uncorrected 14C ages of only 5,111±38 and 5,106±38 yr BP, respectively. We reject these young ages, because they are likely to be overprinted by the adsorption of modern atmospheric carbon dioxide onto the surfaces of the extracted diatom hard parts prior to sample graphitisation and combustion for 14C dating. The deposition of the diatom-rich unit in the western Amundsen Sea suggests deglaciation of the inner shelf before ca. 13 ka BP. The deposition of diatomaceous oozes on other parts of the Antarctic shelf around the same time, however, seems to be coincidental rather than directly related.

Seawater carbonate chemistry and sperm swimming speed of the polychaete Galeolaria caespitosa in lab experiment

The rapidity of ocean acidification intensifies selection pressure for resilient phenotypes, particularly during sensitive early life stages. The scope for selection is greater in species with greater within-species variation in responses to changing environments, thus enhancing the potential for adaptation. We investigated among-male variation in sperm swimming responses (percent motility and swimming speeds) of the serpulid polychaete Galeolaria caespitosa to near- (delta pH 0.3) and far-future ocean acidification (delta pH 0.5). Responses of sperm swimming to acidification varied significantly among males and were overall negative. Robust sperm swimming behavior under near-future ocean acidification in some males may ameliorate climate change impacts, if traits associated with robustness are heritable, and thereby enhance the potential for adaptation to far-future conditions. Reduced sperm swimming in the majority of male G. caespitosa may decrease their fertilization success in a high CO2 future ocean. Resultant changes in offspring production could affect recruitment success and population fitness downstream.

Seawater carbonate chemistry and sperm swimming speed, fertilization success of the Australasian sea urchin Heliocidaris erythrogramma in lab experiment

Background: Climate change will lead to intense selection on many organisms, particularly during susceptible early life stages. To date, most studies on the likely biotic effects of climate change have focused on the mean responses of pooled groups of animals. Consequently, the extent to which inter-individual variation mediates different selection responses has not been tested. Investigating this variation is important, since some individuals may be preadapted to future climate scenarios. Methodology/Principal Findings: We examined the effect of CO2-induced pH changes ("ocean acidification") in sperm swimming behaviour on the fertilization success of the Australasian sea urchin Heliocidaris erythrogramma, focusing on the responses of separate individuals and pairs. Acidification significantly decreased the proportion of motile sperm but had no effect on sperm swimming speed. Subsequent fertilization experiments showed strong inter-individual variation in responses to ocean acidification, ranging from a 44% decrease to a 14% increase in fertilization success. This was partly explained by the significant relationship between decreases in percent sperm motility and fertilization success at delta pH = 0.3, but not at delta pH = 0.5. Conclusions and Significance: The effects of ocean acidification on reproductive success varied markedly between individuals. Our results suggest that some individuals will exhibit enhanced fertilization success in acidified oceans, supporting the concept of 'winners' and 'losers' of climate change at an individual level. If these differences are heritable it is likely that ocean acidification will lead to selection against susceptible phenotypes as well as to rapid fixation of alleles that allow reproduction under more acidic conditions. This selection may ameliorate the biotic effects of climate change if taxa have sufficient extant genetic variation upon which selection can act.