Sea surface temperatures of southern midlatitudes 0–160 kyr B.P.

Abstract

[1] Late Quaternary climate fluctuated between extremes of glaciations, lasting $90 kyr on average, and interglacial episodes, lasting $10 kyr. Still largely unknown are the spatial and temporal evolution of these global climate states, with vigorous debate still underway on the mechanisms responsible for glacial inceptions and terminations. Though it is widely believed that the Southern Hemisphere oceans play a central role in global climate changes, few paleoclimate records exist from there. Here we present three new alkenone-derived SST records from the midlatitude Southern Hemisphere spanning the last 160 kyr, a full glacial-interglacial cycle. Our subtropical SST records from the last glacial period are characterized by (1) warming 47-23 kyr B.P., when high latitudes in both hemispheres cooled, and (2) milder temperatures during the penultimate glacial period than during the last glacial interval. These SST features are found to be of tropical-to subtropical-wide extent, implying increased thermal gradients at times of high-latitude ice sheet growth. This has implications for the vigor of atmospheric and upper ocean circulation and the transport of heat and moisture to the poles that may have been instrumental in the growth and maintenance of polar ice sheets during glacial periods.

Southern Ocean deep convection as a driver of Antarctic warming events

“…All rights reserved. Phanke and Sachs, 2006;Barrows et al, 2007;Lopes dos Santos, 2013]. Applying freshwater/salinity anomalies to the SO surface can bring the temperature response in the model in line with observations , by directly forcing changes in SO overturning; however, the large fluxes of freshwater required are not well-supported by data.…”

Eastern tropical Pacific hydrologic changes during the past 27,000 years from D/H ratios in alkenones

“…Studies of marine core tops and sediment traps demonstrate that alkenones, despite significant differences in seasonal and interannual alkenone export, record mean annual SST [Conte et al, 2006;Müller et al, 1998;Prahl et al, 2005]. It is therefore plausible that mean annual insolation changes may be imprinted on midlatitude to low latitude SSTs as has previously been suggested for the time interval 47 -23 ka [Pahnke and Sachs, 2006]. The amplitude of these insolation changes is small ($3.2 W/m 2 at 5°N) relative to insolation changes at high latitudes.…”

Gas escape features off New Zealand: Evidence of massive release of methane from hydrates

“…This process is similar to active methane release west of Svalbard that has been linked to a down-slope movement of the top of gas hydrate stability since 1970 [Westbrook et al, 2009]. Temperature variations at the sea floor along the Chatham Rise above 1,100 m depth are unknown, but alkenone analysis of core MD972120 (water depth 1210 m) [Pahnke and Sachs, 2006] indicates that glacial-interglacial sea surface temperatures along the southern Chatham Rise could have varied by 3-6°C.…”

“…[12] Sea surface temperatures off Chatham Rise warmed abruptly by about 1°C several times between 35 and 21 ka [Pahnke and Sachs, 2006;Barrows et al, 2007]. At depth, the benthic d 18 O record for AAIW also underwent episodic changes ∼0.25‰ that may represent warming and cooling of ∼1°C [Pahnke and Sachs, 2006].…”