Description: During the past 40,000 years, global climate has moved into and out of a full glacial period, with the deglaciation marked by several millennial-scale rapid climate change events. Here we investigate the ecological response of deep-sea coral communities to both glaciation and these rapid climate change events. We find that the deep-sea coral populations of Desmophyllum dianthus in both the North Atlantic and the Tasmanian seamounts expand at times of rapid climate change. However, during the more stable Last Glacial Maximum, the coral population globally retreats to a more restricted depth range. Holocene populations show regional patterns that provide some insight into what causes these dramatic changes in population structure. The most important factors are likely responses to climatically driven changes in productivity, [O2] and [CO3]2-.

Description: Stable carbon isotope ratios of archaeal glycerol dibiphytanyl glycerol tetraether (GDGT) lipids have been proposed as a proxy to infer past changes in the carbon isotope composition (δ13C) of dissolved inorganic carbon (DIC). The premise for reconstructing paleo-δ13CDIC from GDGTs is based on observations of relatively constant δ13CGDGT values in recent depositional environments. Marine Thaumarchaeota, thought to be the dominant source of GDGTs to marine sediments, fix inorganic carbon using the 3-hydroxypropionate/4-hydroxybutyrate (3HP/4HB) pathway, which is specific to HCO3- as the substrate. Bicarbonate-dependent autotrophy has been the basis for predicting that the stable carbon isotopic composition of GDGTs (δ13CGDGT) should vary in parallel with water column δ13CDIC values, because HCO3- is by far the dominant fraction of DIC in modern seawater. However, this relationship has never been systematically tested. Here we examine the carbon isotopic composition of GDGTs from four water column profiles in the Southwest and Equatorial Atlantic Ocean. Values of δ13CGDGT increase with depth in the water column, in contrast to the characteristic decrease in δ13CDIC values. These divergent trends imply a decrease in the observed total biosynthetic isotope effect (𝜀Ar) with depth, i.e., the offset between δ13CDIC and δ13CGDGT is not constant. Instead, we find that values of 𝜀Ar specifically correlate with oceanographic variables associated with extent of organic remineralization, decreasing as CO2 concentration increases. This observed relationship is consistent in both magnitude and direction with the results of an isotope flux-balance model for Thaumarchaeota that suggests 𝜀Ar should be sensitive to growth rate (µ) and CO2 availability under conditions of atmospheric pCO2 〈 4 times the pre-anthropogenic Holocene level. Further tests of the sensitivity of 𝜀Ar to µ and CO2 in the modern marine environment will be essential to exploring the potential for a new, archaeal lipid-derived pCO2 paleobarometer.

Description: The D14C of surface water dissolved inorganic carbon (DIC) in the Southern California Bight was compared to D14C as recorded by the sterols in Santa Monica and Santa Barbara Basin sediments. All of the C26, C27, C28, and C29 sterols as well as dinosterol had 14C concentrations equal to surface water DIC, indicating that all of the major sterols were derived from phytoplanktonic production. There is no detectable terrestrial component. Their tracer capability was confirmed by comparing the “bomb 14C”-derived change in surface water D14CDIC with the change in D14Csterol. The “prebomb” D14CDIC was -82 per mil, and prebomb sterols averaged -75±19 per mil. The D14C value in 1996 was +71 per mil. Eighteen measurements representing eight different sterols from the sediment-water interface of both Santa Monica and Santa Barbara Basins averaged +62±23 per mil. When three of these values were eliminated because of suspected contamination, the remaining data averaged +71 ±12 per mil. The entire compound class could serve as an excellent proxy for the 14C concentration of ocean surface waters.

Description: Here we report on data from an oceanographic cruise on the German research vessel Meteor covering large parts of the Mediterranean Sea during spring of 2011. The main objective of this cruise was to conduct measurements of physical, chemical and biological variables on a section across the Mediterranean Sea with the goal of producing a synoptic picture of the distribution of relevant physical and biogeochemical properties, in order to compare those to historic data sets. During the cruise, a comprehensive data set of relevant variables following the guide lines for repeat hydrography outlined by the GO-SHIP group (http://www.go-ship.org/) was collected. The measurements include salinity and temperature (CTD), an over-determined carbonate system, inorganic nutrients, oxygen, transient tracers (CFC-12, SF6), helium isotopes and tritium, and carbon isotopes. The cruise sampled all major basins of the Mediterranean Sea following roughly an east-to-west section from the coast of Lebanon through to the Strait of Gibraltar, and to the coast of Portugal. Also a south-to-north section from the Ionian Sea to the Adriatic Sea was carried out. Additionally, sampling in the Aegean, Adriatic and Tyrrhenian Seas were carried out. The sections roughly followed lines and positions that have been sampled previously during other programs, thus providing the opportunity for comparative investigations of the temporal development of various parameters.