Peatland records of dust deposition from Middleton Island, Gulf of Alaska
Abstract
Iron is an important micronutrient that limits the growth of phytoplankton in much of the global ocean. In the Gulf of Alaska (GoA), we have a limited knowledge of the processes that transport iron, and in particular, the role eolian dust plays in delivering iron to the ocean surface. In order to better understand both modern and past mechanisms of dust deposition in the GoA, we examine satellite, NCEP reanalysis, and meteorological station data as well as geochemical data from peat cores collected from Middleton Island (59.43°N, 146.34°W). Widespread dust events have been observed in MODIS satellite imagery emanating from exposed floodplains within the Copper River valley and adjacent glaciated river valleys in southcentral Alaska (AK). Dust events are common in the fall when high pressure in the AK interior and low pressure in the central GoA establish a tight pressure gradient that drives anomalously strong northerly winds. Low river levels and limited snow coverage expose fine-grained glacial sediments that are entrained by winds. MODIS imagery indicates dust reaches beyond the continental shelf, and in many instances, dust plumes have been observed passing over Middleton Island (100 km SSW of the Copper River delta). To better constrain dust deposition from southcentral AK on geologic timescales, we collected cores from an extensive peat bog on Middleton Island, located at the edge of the continental shelf. X-ray imagery, bulk density, magnetic susceptibility, loss on ignition, and profiling XRF data indicate significant variations in inorganic or clastic components within the organic peat matrix. Because these cores were collected near the island's topographic high point, we infer that all inorganic constituents are likely delivered as dust, with potential secondary contributions from volcanic ash. We will present a well-dated, high-resolution scanning XRF profile that spans the last 5200 years and records downcore variations in terrigenous material that are likely related to Copper River dust events.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2011
- Bibcode:
- 2011AGUFMPP23B1847M
- Keywords:
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- 1029 GEOCHEMISTRY / Composition of aerosols and dust particles;
- 3344 ATMOSPHERIC PROCESSES / Paleoclimatology