Expedition 379T Proceedings, Digging Deeper with the JR100: Extending high resolution paleoclimate records from the Chilean Margin to the Eemian

Expedition 379T of the D/V JOIDES Resolution was the first in the new NSF funded JR100 program, intended to provide the US paleoceanographic community a new way for recovering long sediment records (up to 100 meters below seafloor) outside of the IODP program. As such, it bridges between the conventional coring capability on UNOLS ships and the deep sea drilling program. The primary objective of the expedition was to investigate links between oceanographic changes at the northern margin of the Antarctic Circumpolar Current and climate variability on the South American continent over the past few glacial-interglacial cycles, with a special emphasis on obtaining high-resolution records of the Eemian interval and the last two glacial terminations. Given very high sedimentation rates along the Chilean margins, the new cores will enable reconstruction of surface and intermediate water variability at centennial-to-millennial resolution, which will extend available records from previous coring expeditions (ODP Expedition 202), thus permitting comparison of Southern Hemisphere records of the Holocene and last interglacial (LIG- Eemian), terminations I and II, and the MIS 5e-5d glacial inception. 

Eight sites were cored during Expedition 379T, recovering a total of 2232 m of sediment cores in 670–3055 m water depth with an average recovery of 101.8% during 14.62 days of on-site operations (Table T1). Despite delayed departure at Punta Arenas and several bad weather days that prevented us from coring some of the planned sites, we have achieved almost all the expedition objectives. The eight sites extend over a wide latitudinal distance (46-36°S) covering the modern transition from the Antarctic subpolar to the subtropical zones (Figure F1) as well as spanning water depths intersecting the Antarctic Intermediate Water (AAIW), Pacific Deep Water (PDW) and Circumpolar deep water (CPDW) water masses (Figure F2).  Six of the sites are located on the Chilean margins at intermediate water depths (670-1534 mbsl) and the other two sites are situated in deep water off the shelf (2032 and 3055 mbsl).  Three holes were APC cored in all but one site (J1003 has only two holes) allowing for compositing complete splices for paleoceanographic reconstructions (Figure F3). Shipboard analyses of the sediment cores included determining properties including magnetic susceptibility (MS), gamma ray attenuation (GRA), natural gamma radiation (NGR), visual description and imaging, paleomagnetic measurements, and micropaleontology (foraminifers, nannofossil and diatoms).  Low-resolution (1 per core) interstitial water samples were collected for shipboard elemental analysis at each site.  In addition, high-resolution interstitial water samples (1 per section) were collected at each site for further shore-based isotopic and elemental investigations totaling 472 IW samples.

Of the 30 science-party members we had 15 graduate students and 7 postdocs, assisted by 6 senior scientists. All members of the science-party were trained in and carried out the shipboard analyses, and contributed to the interpretations and report writing. We adopted the report format used on IODP expeditions to ensure future users of the cores have all the necessary information to interpret the wealth of data collected onboard; we recommend that this be done on future JR100 expeditions. Finally, two undergraduate students were trained by the technical staff, and two Chilean observers both fully participated in the shipboard analyses.  It is our opinion that the educational component is another important strength of the JR100 program.