On Using Si to Unravel Potential Sources of Dissolved Al to the Deep Arctic. Issue 10 (13th October 2021)

• Record Type: Journal Article
• Authors: Measures, C. I.; Hatta, M.
• Is Part Of: Journal of geophysical research. Volume 126:Issue 10(2021)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2021-10-13
• Subjects: aluminum -- Arctic Ocean -- deep water -- silicic acid -- slope processes -- turbidity currents; Oceanography -- Periodicals; 551.4605
• DOI: 10.1029/2021JC017399
• Languages: English
• ISSNs: 2169-9275

Abstract

Abstract: An examination of the vertical profiles of aluminum, silicic acid, and the Si:Al ratio indicates that the enrichment of dissolved Al in the bottom waters of the Arctic basins cannot be explained by the water column remineralization of vertically transported biological material. Instead, it is suggested that the bottom water enrichments are a result of the dissolution of amorphous aluminosilicates that are produced within the sedimentary pore waters by a reverse weathering process. We suggest that these materials are released into the low Si, low Al overlying water column by turbidity currents descending from the broad Arctic shelves which deliver sediments, water, and the products of reverse weathering into the bottom waters of the Arctic basins. It is suggested that from its delivery point at the basin edges, this dissolved Al signal then spreads out, enriching the signals in the bottom of the basins and mixes upward into the overlying water column to produce the observed vertical gradients. Thus, the deepwater Al enrichment is driven by a concentration gradient from below, that is, it is a bottom up (sedimentary driven), rather than the top down (particle export) process that has been previously suggested. It is also suggested that this dissolved Al signal might potentially be used as a tracer of these sporadic turbidity events, which in addition to transporting sediments, also are a mechanism for subducting water into abyssal regions. The observation of elevated dissolved Al signals at other ocean boundaries adjacent to Al‐rich lithogenic materials further suggests that the formation of the products of reverse weathering within sediments is probably widespread along continental margins. Plain Language Summary: The elevated levels of dissolved aluminum (Al) and dissolved silicon (Si) seen in the bottom waters of the Arctic Ocean basins are a result of the release of materials that form within the sediments from chemical reactions between dissolved Al and Si (reverse weathering). We hypothesize that fast flowing dense submarine flows comprised of sediments entrained in water (turbidity currents), similar to an avalanche, carry this material to the bottom of the Arctic basins, where it is released into the water column and dissolves, providing the observed Al and Si enrichments. The gradients in chemical properties seen in the water column of the Arctic are then a result of a bottom up (sediment driven) process rather than a top‐down (surface water particle export) process. The dissolved Al signal may become a tracer of the fairly rare turbidity currents as well as the water that accompanies them. The occurrence of similar Al enrichments in deep water along the edges of continents suggests that the formation of reverse weathering products within the sediments is a widespread phenomenon. Key Points: Elevated dissolved aluminum was observed throughout deep waters of the Canada, Makarov, and Amundsen Basins The deep Si:Al molar ratio decreased with increasing maximum basin depth, from the Canada to the Makarov to the Amundsen Basin Dissolution of amorphous aluminosilicates formed within pore waters and coated to resuspended sediments introduced to bottom waters by turbidity currents is the most likely mechanism leading to the observed dissolved Al and Si:Al ratios of deep Arctic waters