Eolian deposition of glacial flour dust to the Gulf of Alaska during the Holocene
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 combine satellite, meteorological, and geochemical data from peat cores collected on Middleton Island (59.43°N, 146.34°W). Middleton Island is located on the edge of the continental shelf and is well-located to monitor the flux of particulate material into adjacent Fe-limited waters. 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). These events are most common in the fall when high pressure in the AK interior and low pressure in the central GoA establish a pressure gradient that drives anomalously strong northerly winds that entrain fine-grained glacial sediments exposed along Copper River floodplains. MODIS imagery indicates that 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 to the GoA during the Holocene, we collected cores from an extensive peatland on Middleton Island. Loss-on-ignition and profiling XRF data indicate significant variations in inorganic or clastic components within the organic peat matrix during the last 5,300 cal yr BP. Clastic content varies between 2 and 45% and is particularly elevated during the last 1,500 years of the record. Ti variations closely mirrors clastic content, and 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. In addition, bulk organic δ15N exhibits 15 parts per mill variability, which closely tracks variations in clastic content and Ti. The N isotope co-variation with clastic content could either reflect the isotopic composition of the eolian source material or may reflect a local vegetation response to increased delivery of clastic material. Overall, multiple proxies point toward increased eolian deposition after 1,500 cal yr BP that culminates between 600 and 200 cal yr BP. Given Middleton Island's proximity to Fe-limited waters, our record provides important constraints on the continental input to the northern GoA during the late Holocene.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2012
- Bibcode:
- 2012AGUFMPP22A..05M
- Keywords:
-
- 1029 GEOCHEMISTRY / Composition of aerosols and dust particles;
- 1616 GLOBAL CHANGE / Climate variability;
- 4904 PALEOCEANOGRAPHY / Atmospheric transport and circulation