Abyssal zone

Abstract: From the time that detailed oxygen isotope records derived from foraminifera living in the constant-temperature environment of the abyssal ocean became available, there has been a discrepancy between the ice volume record that these records imply, and that derived from the altitude of dated coral terraces around the world. Here, we re-examine the data and conclude that the temperature of the abyssal ocean has been an actively varying component of the climate system.

Abstract: Ocean microstructure data show that turbulent mixing in the deep Brazil Basin of the South Atlantic Ocean is weak at all depths above smooth abyssal plains and the South American Continental Rise. The diapycnal diffusivity there was estimated to be less than or approximately equal to 0.1 x 10(-4) meters squared per second. In contrast, mixing rates are large throughout the water column above the rough Mid-Atlantic Ridge, and the diffusivity deduced for the bottom-most 150 meters exceeds 5 x 10(-4) meters squared per second. Such patterns in vertical mixing imply that abyssal circulations have complex spatial structures that are linked to the underlying bathymetry.

Abstract: Changes in oxygen concentrations at the sediment-water interface play a major role in controlling benthic foraminiferal assemblages and morphologic characteristics; such changes are reflected in size, wall thickness, porosity, and also taxa (genera and species) of foraminifera present. These morphologic and taxonomic differences have been quantified as a dissolved-oxygen index. This paper demonstrates that the foraminiferal oxygen index derived from bathyal and abyssal Holocene faunas correlates well with the dissolved-oxygen levels in overlying waters. This index is then used for paleoenvironmental interpretations.

Abstract: AbyssalglobalanddeepSouthern Oceantemperature trendsarequantifiedbetweenthe1990sand2000sto assesstheroleofrecentwarmingoftheseregionsin globalheatandsealevelbudgets.Theauthors1)compute warming rates with uncertainties along 28 full-depth, high-quality hydrographic sections that have been occupied two or more times between 1980 and 2010; 2) divide the global ocean into 32 basins, defined by the topography and climatological ocean bottom temperatures; and then 3) estimate temperature trends in the 24 sampled basins. The three southernmost basins show a strong statistically significant abyssal warming trend, with that warming signal weakening to the north in the central Pacific, western Atlantic, and eastern Indian Oceans. Eastern Atlantic and western Indian Ocean basins show statistically insignificant abyssal cooling trends. Excepting the Arctic Ocean and Nordic seas, the rate of abyssal (below 4000 m) global ocean heat content change in the 1990s and 2000s is equivalent to a heat flux of 0.027 (60.009) W m 22 applied over the entire surface of the earth. Deep (1000‐4000 m) warming south of the Subantarctic Front of the Antarctic Circumpolar Current adds 0.068 (60.062) W m 22 . The abyssal warming produces a 0.053 (60.017) mm yr 21 increase in global average sea level and the deep warming south of the Subantarctic Front adds another 0.093 (60.081)mm yr 21 . Thus, warmingin theseregions,ventilatedprimarilyby AntarcticBottomWater,accounts for a statistically significant fraction of the present global energy and sea level budgets.