Geochemistry of sediment cores of the Southern Ocean

We examine the possibility that glacial increase in the areal extent of reducing sediments might have changed the oceanic Cd inventory, thereby decoupling Cd from PO4. We suggest that the precipitation of Cd-sulfide in suboxic sediments is the single largest sink in the oceanic Cd budget and that the accumulation of authigenic Cd and U is tightly coupled to the organic carbon flux into the seafloor. Sediments from the Subantarctic Ocean and the Cape Basin (South Atlantic), where oxic conditions currently prevail, show high accumulation rates of authigenic Cd and U during glacial intervals associated with increased accumulation of organic carbon. These elemental enrichments attest to more reducing conditions in glacial sediments in response to an increased flux of organic carbon. A third core, overlain by Circumpolar Deep Water (CPDW) as are the other two cores but located south of the Antarctic Polar Front, shows an approximately inverse pattern to the Subantarctic record. The contrasting patterns to the north and south of the Antarctic Polar Front suggest that higher accumulation rates of Cd and U in Subantarctic sediments were driven primarily by increased productivity. This proposal is consistent with the hypothesis of glacial stage northward migration of the Antarctic Polar Front and its associated belt of high siliceous productivity. However, the increase in authigenic Cd and U glacial accumulation rates is higher than expected simply from a northward shift of the polar fronts, suggesting greater partitioning of organic carbon into the sediments during glacial intervals. Lower oxygen content of CPDW and higher organic carbon to biogenic silica rain rate ratio during glacial stages are possible causes. Higher glacial productivity in the Cape Basin record very likely reflects enhanced coastal up-welling in response to increased wind speeds. We suggest that higher productivity might have doubled the areal extent of suboxic sediments during the last glacial maximum. However, our calculations suggest low sensitivity of seawater Cd concentrations to glacial doubling of the extent of reducing sediments. The model suggests that during the last 250 kyr seawater Cd concentrations fluctuated only slightly, between high levels (about 0.66 nmol/kg) on glacial initiations and reaching lowest values (about 0.57 nmol/kg) during glacial maxima. The estimated 5% lower Cd content at the last glacial maximum relative to modern levels (0.60 nmol/kg) cannot explain the discordance between Cd and delta13C, such as observed in the Southern Ocean. This low sensitivity is consistent with foraminiferal data, suggesting minimal change in the glacial Cd mean oceanic content.

DNA alignment and Bayesian trees of partial sequences of COI, COIII and the haemocyanin functional unit f-g of 28 octopod species

Background: Octopods have successfully colonised the world's oceans from the tropics to the poles. Yet, successful persistence in these habitats has required adaptations of their advanced physiological apparatus to compensate impaired oxygen supply. Their oxygen transporter haemocyanin plays a major role in cold tolerance and accordingly has undergone functional modifications to sustain oxygen release at sub-zero temperatures. However, it remains unknown how molecular properties evolved to explain the observed functional adaptations. We thus aimed to assess whether natural selection affected molecular and structural properties of haemocyanin that explains temperature adaptation in octopods. Results: Analysis of 239 partial sequences of the haemocyanin functional units (FU) f and g of 28 octopod species of polar, temperate, subtropical and tropical origin revealed natural selection was acting primarily on charge properties of surface residues. Polar octopods contained haemocyanins with higher net surface charge due to decreased glutamic acid content and higher numbers of basic amino acids. Within the analysed partial sequences, positive selection was present at site 2545, positioned between the active copper binding centre and the FU g surface. At this site, methionine was the dominant amino acid in polar octopods and leucine was dominant in tropical octopods. Sites directly involved in oxygen binding or quaternary interactions were highly conserved within the analysed sequence. Conclusions: This study has provided the first insight into molecular and structural mechanisms that have enabled octopods to sustain oxygen supply from polar to tropical conditions. Our findings imply modulation of oxygen binding via charge-charge interaction at the protein surface, which stabilize quaternary interactions among functional units to reduce detrimental effects of high pH on venous oxygen release. Of the observed partial haemocyanin sequence, residue 2545 formed a close link between the FU g surface and the active centre, suggesting a role as allosteric binding site. The prevalence of methionine at this site in polar octopods, implies regulation of oxygen affinity via increased sensitivity to allosteric metal binding. High sequence conservation of sites directly involved in oxygen binding indicates that functional modifications of octopod haemocyanin rather occur via more subtle mechanisms, as observed in this study.

Annotated record of the detailed examination of Mn deposits from R/V Robert Conrad Cruise 05 stations

The cores described in this report were taken during the R/V Robert Conrad Cruise 05 from March until April 1963 by the Lamont Geological Observatory, Columbia University. A total of 13 cores were recovered and are available at Lamont-Doherty Earth Observatory for sampling and study.

Annotated record of the detailed examination of Mn deposits from R/V Robert Conrad Cruise 02 stations

The cores described in this report were taken during the R/V Robert Conrad Cruise 02 from 26 until 28 January 1963 by the Lamont Geological Observatory, Columbia University. A total of 5 cores were recovered and are available at Lamont-Doherty Earth Observatory for sampling and study.