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.
This collaborative project funded a research cruise aboard the R/V Marcus G. Langseth from May 1 to May 26, 2013 to survey the Line Islands Ridge and obtain sediment cores for paleoceanographic research. The research cruise was led by co-chief scientists Jean Lynch-Stieglitz (Ga. Tech) and Pratigya Pollisar (LDEO), in collaboration with fellow researchers Mitch Lyle (TAMU), Rob Pockalny (GSO/URI), Rick Murray (Boston U.), Steve Hovan (IUP), Katherine Wejnert (Ga. Tech.), Samantha Bova (Brown), Victor Castro (UCSC), Ann Dunlea (Boston U.), Heather Ford (UCSC), Jennifer Hertzberg (TAMU), Allison Jacobel (LDEO), Christina King (GSO/URI), Ashley Maloney (UW), Julia Shackford (TAMU), and Ruifang Xie (TAMU). The research cruise started and finished in Honolulu, Hawaii and traveled over 7,000 km, mapped over 100,000 km2 of seafloor, collected 147 m of sediment with an array of 41 piston, trigger, gravity and multi-core corers, and deployed 14 CTD/Niskin rosette casts for water column samples (see attached figures for shiptrack and numbered coring locations). Geophysical survey data (multibeam bathymetry/backscatter, and sub-bottom CHIRP and multi-channel seismics) were processed at sea and used to select coring sites. Non-destructive analyses (e.g., MST core logging, and core break paleontological analyses) of the sediment cores were performed onboard and cores were then archived/curated for future shore–based analyses. Our preliminary cruise results indicate that the Line Islands Plateau above 2000 m water depth is covered by mostly smooth sediments, which are cut by an occasional dendritic channel. In some places the sediments were as thick as 1.2 km, but volcanic features also protruded through the sediment surface. Evidence for strong current activity included smooth surfaces, sediment waves, and large sediment drifts in the lee of volcanic features. Attempts to core these sediments suggested that these sediments are composed primarily of winnowed foraminifera sands. The sediments below 2000 m water are typically marked by erosion. The style of erosion varied, from gently stepping incised terraces near the equator, to more mature looking dendritic channels further north. In general, the ridge tops between channels showed low backscatter on the multibeam suggesting recent sedimentation, and the sides and bottoms of the channels showed higher backscatter suggesting sandy/harder ground. Multi-channel seismic reflection surveys across the channels show them to be eroded into older sediment. Coring sites were chosen at water depths of 2500-3500 m on local highs or ridges in between the more deeply eroded channels. Multi-cores, gravity cores, and piston cores were collected. Sediments consist mainly of carbonate oozes dominated by foraminiferal and nanofosssil components. The goals of the Intellectual Merit section of the proposal are: 1. This project will obtain new material for geochemical and micropaleontological studies of changes in the Pacific Marine (Intertropical Convergence Zone) ITCZ and (El Niño–Southern Oscillation) ENSO over glacial and orbital cycles (time scales of 10-100 kyr), and which can be used to constrain ocean-atmosphere models of climatic change. 2. It may provide new material from the last 10,000 years, which can be used to provide perspective to ongoing work from corals and lake sediments on the Line Islands. 3. It may provide information, which can lead to future long coring or drilling efforts to understand changes in the ITCZ over longer time scales (millions to tens of millions of years). Initial results strongly suggest we have obtained geophysical data and sediment samples that will allow us to achieve our goals. Shipboard estimates of sedimentation rate (1-4 cm/kyr) and sediment age (300-500 kyrs) are consistent with samples required to address goals #1 and #2. The geophysical data provide extremely useful spatial coverage and sub-bottom characterization to identify preliminary targets for future coring and drilling operations in the region, which addresses goal #3. The Broader Impacts of the proposal are: 1. This project will provide sample material for 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 previously unexplored parts of the seafloor. 2. It will enhance scholarly exchange between the participating institutions, interface with a multi-agency federal program, and contribute to centralized and federally supported oceanographic databases. 3. It will introduce graduate students to seagoing paleoceanography, and enhance public dissemination of scientific research. All three Broader Impact goals have been met and in many instances we have gone well beyond these stated goals. In addition to obtaining sediment samples for ITCZ and ENSO studies, we have also obtained sediment and water samples for numerous related studies. Cruise results and data have been made public to the research community. In addition, we have provided geophysical data to the Kiribati government for Law of the Sea Treaty proposal preparation and data plots to the U.S. State Department for use in planning future efforts for the Extended Continental Shelf Project.
