The North Atlantic plays a critical role in heat transport in the ocean-atmosphere system because it is an area of deep water formation where surface waters sink to produce the North Atlantic Deep Water (NADW). Surface water temperature and salinity define the strength of the NADW in the conveyor circulation and consequently the strength of the Atlantic meridional overturning circulation (AMOC). For this project, we are studying thermal history of the western North Atlantic during the critical climate transition of 17-12.8 Ma and the role of the North Atlantic in the global climate change during the middle Miocene. Previous work in the North Atlantic has focused on benthic foraminiferal δ18O and δ13C tracers to study deep water and isolate temperature vs. ice volume signal for the Oligocene-upper Miocene (e.g., Miller et al., 1985; Wright et al., 1992). We are enhancing existing records of benthic foraminifera by performing stable isotopes and trace metals (Mg/Ca) analyses on planktonic foraminifera and obtaining sea surface temperatures from organic paleothermometers TEX86 and UK'37. Integration of these multiple proxies is essential in deciphering paleotemperature signals from those of ice volume and salinity.
Mitch Lyle (OSU) Greg Mountain, Ken Miller, have a pending International Ocean Discovery Program (IODP) Expedition in the Western North Atlantic. Proposal 851-Pre is designed to drill to monitor the evolution of northern deep waters (Northern Component Water, NCW), changes in sea surface temperature (SST), thermocline structure, and meridional thermal gradients in the North Atlantic subtropical and subarctic gyres, and changes in biogeochemical cycling and biogenic production through the Miocene and into the Paleogene. The proposal is up for scheduling by the IODP JOIDES Resolution Facilities Board if IODP is extended .
What’s next: Undergraduate honors theses by M. Galochkina is being prepared for publication. Studies of Site 982 are being completed. The next step is to do high resolution (10 cm, 10 kyr) sampling of a Miocene time slice for stable isotopes and correlating with XRF core scans.