The project will investigate abrupt and high-frequency climate change at an ultra-high resolution previously unobtainable before 150 ka, but here spanning most of the 100-kyr climate regime back to ~700 ka. Resolving short-term climate behavior before ~150 ka is critical for understanding processes, thresholds, and feedbacks that contribute to abrupt climate change. Millennial-scale climate oscillations (Dansgaard/Oeshger cycles) reflect major abrupt shifts in the ocean-atmosphere system, yet knowledge of this important behavior is largely confined to the last glacial cycle, owing to the unavailability of suitable older sequences. This study will extend the understanding of these events and processes for the first time by analysis of a superb suite of 32 high-sedimentation rate (~80-120 cm/kyr) cores taken in 2005 on the Santa Barbara Mid-Channel anticlinal trend, where older, uplifted stratigraphic sequences crop out on the ocean floor. The PIs preliminary work confirms that Santa Barbara Basin can reveal climate history in unprecedented resolution for this time span, clearly recording earlier D/O-like cycles and abrupt climate change on decadal time scales. The cores provide ultra-high resolution windows into climatic-oceanographic behavior of the north Pacific through much of the interval dominated by the 100 kyr glacial-interglacial cycles, an interval not previously studied at this resolution.
The broader impacts of this study include incorporating Graduate and undergraduate students at three universities will be involved in all aspects of the study. This project will fund (2-3) graduate students to work at CSULB and UC Davis on the paleoclimatic and paleoceanographic investigations based on the geochemical, faunal, and sedimentologic analyses of the cores. This project provides funds for training and support of undergraduates (5-10 total) in laboratory work and research projects at the three institutions. The program will incorporate students from NSF-targeted underrepresented groups as part of the undergraduate research component of the NSF-funded Geoscience Diversity Enhancement Program at CSULB. All three researchers in this project have a track record of incorporating climate change topics into frequent presentations for large undergraduate courses and the public.
Understanding abrupt and fluctuating climate change and its relationship with oceanic and biological processes is critical to our ability to address current and future climate change. Although there has likely been great variety in the background conditions, triggers and behavior of such changes, there is little knowledge of rapid change prior to the last glacial cycle (<60 kyr). This NSF-funded collaborative project acquired and analyzed a suite of >30 sediment cores from subsea outcrops in the Santa Barbara Basin (SBB) that allowed us to discover and investigate a number of millennial- to submillennial-scale climate and oceanographic oscillations in sea surface temperature, water column character and structure, and marine sediment geochemistry that extends back to the Mid-Pleistocene, ~735 ka. During this time frame, the duration and magnitude of longer glacial-interglacial cycles transformed, so these records provide "windows" into past climate and ocean behavior and an evaluation of how they may have evolved. We have completed detailed studies of cores that date 0-35 ka, ~293 ka, ~450 ka, 639 ka, and ~735 ka at consistently high sedimentation rates (~ 80-100 cm/kyr), permitting decadal-scale resolution of intervals of rapid change, that include oxygen isotopic composition of different species of planktonic foraminifera that record different depths in the water column, quantitative benthic foraminiferal assemblage analysis, total organic carbon (TOC), calcium carbonate (CaCO3), biogenic silica (BSi), bulk sediment geochemistry, bulk wet density (BWD), color and sediment fabric. The stable isotopic composition of planktonic foraminifera shows millennial-scale climate variability in all three intervals with rapid (decadal-scale) transitions between warm interstadials and cold stadials. Interstadials lasted ~250-1600 years and occurred every ~650-1900 years. Paleotemperatures were 3.5-9.5°C during stadials and 7.5-13°C during interstadials. In these cores, variations of BWD, TOC, BSi, sediment fabric, and to a lesser degree CaCO3 and sediment color, correlate well with climatic oscillations, hence shallow and deep ocean life, oceanic circulation, biogeochemical transport, and the geosphere all responded sensitively to climate change. During warm, laminated intervals, TOC and BSi increased while BWD decreased. Preservation of laminations (exclusion of benthic macrofauna from the seafloor) appears to be associated with a threshold of > 1.5 wt % TOC. Distinct increases in concentrations of redox-sensitive trace elements such as molybdenum and uranium, and productivity proxies such as Cadmium are associated with climatic shifts to warmer conditions, along with higher TOC, BSi and sediment lamination. These relationships suggest increased upwelling, high primary productivity and intense oxygen depletion in bottom waters during warm interstadials. This study builds upon previous work that shows that millennial-scale shifts were an inherent feature of Northern Hemisphere glacial climates since 735 ka, and they remained remarkably constant in the details of their amplitude, cyclicity, and temperature variability. The oxygen minimum zone (OMZ) of the late Quaternary California margin experienced abrupt and dramatic changes in strength and depth in response to changes in intermediate water ventilation, ocean productivity, and climate at orbital through millennial time scales. We integrated information from the new climatic windows back to 735 ka with an ultra-high resolution analysis of two younger cores previously acquired by the IMAGES program that span the past 34 kyr and the last transition from ice age to the interglacial Holocene. Past expansion and contraction of the OMZ is exhibited at high temporal resolution (~100 yr) by quantitative benthic assemblage changes in piston cores forming a vertical profile through the water column in and outside of Santa Barbara Basin from ~1000 to 400 meters water depth. From these data, we extract information on the changing community structure (density, diversity, evenness) to improve paleoenvironmental interpretation and quantify variation in the OMZ by a new dissolved oxygen index based on documented relations between species and water-mass oxygen concentrations. During the last glacial termination at 14.7 ka (Bølling-Allerød), a distinctive suite of benthic fauna appeared across the transect, recording hypoxic waters (< 0.5 ml L-1) < 300 m from the ocean surface. These assemblages uniquely stand out in the record, exhibited by low density, diversity and evenness, and taxonomic composition reflecting extreme and stressful hypoxia and methane-rich environments. Shorter decadal intervals were so severely oxygen-depleted that no benthic foraminifera were present, even those that usually survive within low oxygen levels by symbiosis. This project has provided substantial educational opportunities for young faculty, post-docs, graduate and undergraduate students by supporting their research, training them in laboratory techniques, and taking them to sea on scientific expeditions to acquire seismic data and sediment cores. Five Masters theses have been completed, one PhD dissertation is substantially advanced, and several undergraduate and graduate students in the program were stimulated to pursue PhD’s. A total of 63 undergraduate and graduate students, post-docs, and faculty from 9 different academic institutions have benefited by participating in the NSF-funded Santa Barbara Basin research program (and the two science expeditions in 2005 and 2008) since its inception in 2004.
