Past changes in the behavior of two key features of the global climate, the Intertropical Convergence Zone (ITCZ) and the El-Nino Southern Oscillation (ENSO), are not clearly understood at present. Continuous records from marine sediments are needed to inform paleoreconstructions of these and other climatic and oceanographic patterns during the Holocene. This project will attempt to acquire such records from the Line Islands Ridge in the Central Tropical Pacific, a key and sensitive location with little in terms of existing samples or data.
The Line Islands Ridge is an ideal site to capture paleooceanographic and paleoclimatic changes recorded in sediment for a number of reasons. First, the ITCZ and ENSO are not as susceptible to seasonal or spatial variation in this region as they are elsewhere. In addition, because the Line Islands Ridge is a bathymetric high, the calcium carbonate shells that contain the paleoenvironmental proxy indicators are less likely to be affected by dissolution than in nearby deep ocean settings.
Researchers at the Georgia Institute of Technology, Columbia University's Lamont-Doherty Earth Observatory, the Graduate School of Oceanography at the University of Rhode Island, Texas A&M University, Boston University, and the University of California at Santa Cruz will collaborate to conduct a reconnaissance coring survey of the Line Islands Ridge. During a research cruise aboard the R/V Langseth, the PIs will collect bathymetric and geophysical data to constrain optimal coring locations; once optimal locations are established, they will collect a suite of physical samples (an initial gravity core, a CTD/Niskin rosette cast, a piston core, and a multi-core) at each site. Analyses of the cores will include determination of sediment composition using scanning XRF, as well as development of stratigraphic and age models using oxygen isotopes from planktonic foraminifera.
Cores and associated data from this reconnaissance effort will be made available to the broader community in order to facilitate future research on paleoclimatic and -oceanographic change over scales of tens to hundreds of thousands of years. Experts in the field foresee using these datasets to better understand past changes in ITCZ and ENSO behavior, sea surface temperature, ocean chemistry, productivity, nutrient and sediment cycling, and eolian dust inputs in the region. Furthermore, these datasets will provide additional opportunities to calibrate paleoclimate models, and may be used to support a geographically overlapping US State Department initiative (Law of the Sea?Extended Continental Shelf program). Additional broader impacts include enhancing scientific infrastructure and disseminating information by adding physical data (cores) to the LDEO sample repository, cataloguing samples through SESAR (System for Earth Sample Registration), and contributing the associated datasets to widely accessible databases (SedDB, NCDC). This project will also involve training for several graduate students. Finally, the multi-faceted approach of this project will provide NSF with an opportunity to evaluate the multi-purpose functionality of the R/V Langseth.
Overview This project supported an oceanographic research expedition to the Line Islands region in the central Equatorial Pacific Ocean. The objectives of the proposal were to: Survey selected areas of the Line Islands Ridge using multi-channel seismic reflection, 3.5kHz subbottom profiler and multibeam bathymetry to identify promising locations for collecting cores suitable for paleoceanographic research Acquire new piston, gravity and multicores in the central equatorial Pacific along a meridional transect Perform on-board and shore-based analyses in order to determine the stratigraphic integrity, sediment age and sedimentation rate of the cores to support further research on the sediment cores by interested parties. Between May 1 and 26, 2012, a 28-day oceanographic expedition to the Line Islands aboard the R/V Marcus G. Langseth sailed from Honolulu, Hawaii to the Line Islands and back. Sediment cores were transported to the Lamont-Doherty Earth Observatory Core Repository where they were photographed and curated and are freely available for sampling and further research. Post-cruise analysis of the oxygen isotope composition of planktonic foraminifera from a subset of the sediment cores has allowed us to tie our shipboard stratigraphy to the global changes in seawater δ18O that occured from the waxing and waning of Earth’s ice ages. These correlations have largely confirmed the shipboard assessments of sedimentation rates and core ages and provide a regional stratigraphy for further work on the cores. Intellectual Merit There now exist a suite of deep-sea cores along a north-south transect in the central Pacific Ocean that are suitable for paleoceanographic research. These cores span a key latitudinal gradient from the equatorial upwelling region in the south across the intertropical convergence zone to the north. Preliminary stratigraphic information, dating and geochemical analyses enhance their utility for future studies. The sediment cores acquired and preliminary analyses from this project provide new material for geochemical and faunal studies of changes in Pacific Ocean atmospheric and oceanic climate over the past 300,000 years. These studies will include investigations of the El Niño-Southern Oscillation and the intertropical convergence zone, major oceanic and atmospheric phenomenon that today play a significant role in determining global and regional climate patterns. The acquisition of sediment cores from the Line Islands is significant as it demonstrates that high-quality deep-sea sediment cores can be acquired from topographic highs in the ocean where sediment disturbances from strong currents, landslides and other transport processes could potentially have distorted the original stratigraphy. Future oceanographic expeditions will benefit from this finding as there are many parts of the ocean where carbonate sediments essential for paleoceanographic research are only preserved on similar topographic highs. Broader Impacts The sediment cores and the data generated are freely available as a community resource for further research and investigation. These materials and data will be used by numerous investigators interested in the history of climate and productivity in the Tropical Pacific, and provide much new information about the geology and sedimentology of this previously unexplored region of the seafloor. The research activities provided sea-going experience for nine graduate and one undergraduate student and one post-doctoral researcher, including a member of an underrepresented group. This exposure is essential to ensuring a strong and diverse ocean-science research community in the future. These students and researchers worked intimately with senior research scientists, learning all aspects of oceanographic exploration and sediment coring. They also participated in initial assessment of the sediment cores, core description and sampling, water collection and sampling and other research activities during the expedition. Ninety percent of the pre-tenure participants were women and 33% of the proponents of the research were women. Results from the expedition and post-expedition analyses have been disseminated to the broader research community and public through publication of a cruise report, sharing of scientific data, presentations at the Fall 2012 and 2013 American Geophysics Union national meetings, and a blog about the cruise (http://blogs.ei.columbia.edu/tag/future-el-nino/). The cruise report and all data collected on the expedition and the post- expedition analyses are available on the expedition website at http://shadow.eas.gatech.edu/ ~jean/ Line_Islands/ Cruise_main.html. All shipboard data (multi-beam bathymetry, multi-channel seismic, 3.5 kHz sub-bottom profiler, CTD cast etc.) were transmitted to the appropriate public data repositories as part of the R2R (rolling deck to repository) program and are freely available to the government, scientists and the general public. In addition, the high-resolution bathymetry, sub-bottom profiling and seismic data collected during the research expedition contribute to the United State’s Extended Continental Shelf Project.
