The late Quaternary history of primary productivity in the subarctic East Pacific

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Author(s): McDonald, Darcy
Source: 201p. Institution: University of British Columbia, Vancouver, BC, Canada
Note: In English. Includes two appendices. 180 refs. Master's thesis
Summary: Palaeoceanographic work in the subarctic northeast Pacific has previously been limited by the common presence of turbidites and by the relatively shallow CCD. ODP Site 887 is on the Patton Murray Rise, an elevated plateau which is largely isolated from these effects. This area is centered under the Alaska Gyre, a region characterized by the domal upwelling of nutrient-rich waters. Sections from Holes 887A and 887C were spliced into the δ18O profile to obtain a continuous composite record. Although calcite is not continuously distributed throughout the drilled section, the benthic foram δ18O profile from this record closely reflects the global (SPECMAP) signal. Hence, based on δ18O data and on radiocarbon dates from site survey cores, a detailed chronology spanning the past 750 ky was developed. The controls on productivity in this region remain unclear since nitrate is perennially present in excess and does not limit primary production. However, past increases in productivity and rapid settling of biogenic matter are suggested by the episodic accumulation of diatomaceous oozes, and by high-resolution Si/Al, Ba/Al, C13org, and CaCO3 profiles. Moreover, episodic shoaling of the redox boundary produced by increased organic matter flux to the seafloor, as during the deposition of the diatomaceous oozes, is suggested by trace metal and Mn enrichments. Significant δ13Corg maxima in the major diatomaceous bands suggest that productivity events have occurred which were sufficient to draw down mixed-layer PCO2. Thus, in contrast to the near-neutral ocean-atmosphere PCO2gradient which exists today, an episodic sink for atmospheric CO2 may have existed in the Gulf of Alaska in the past. Surface water temperature and salinity effects are evident in negative regional surface water δ18O variations. The episodes of enhanced productivity at Site 887 occur synchronously with such δ18O local excursions, suggesting a direct link to low salinity and/or warming events in the Gulf of Alaska which occur on sub- Milankovitch timescales. This suggests that significant climate variability in the Gulf of Alaska has been superposed on glacial-interglacial cycles through the Brunhes Chron. Temporal variations in the availability of iron may also have played a key role in constraining export production through time. Episodic input of iron, which may have stimulated productivity, may have occurred from either Asian sources via the atmosphere or more local sources via meltwater input
Year of Publication: 1997
Research Program: ODP Ocean Drilling Program
Key Words: 24 Surficial Geology, Quaternary Geology; Alaska Gyre; Algae; Antarctica; C-13/C-12; Carbon; Carbon dioxide; Cenozoic; Diatoms; East Antarctica; East Pacific; High-resolution methods; Isotope ratios; Isotopes; Leg 145; Microfossils; North Pacific; Northeast Pacific; Nutrients; O-18/O-16; ODP Site 887; Ocean Drilling Program; Organic carbon; Oxygen; Pacific Ocean; Paleo-oceanography; Paleoatmosphere; Paleoenvironment; Paleotemperature; Patton Murray Rise; Plantae; Productivity; Quaternary; Stable isotopes; Turbidite; Upper Quaternary; Upwelling
Coordinates: N542155 N542155 W1482647 W1482647
Record ID: 2016008201
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