On Using Si to Unravel Potential Sources of Dissolved Al to the Deep Arctic

• Published in: Journal of geophysical research. Oceans 2021-10, Vol.126 (10), p.n/a
• Main Authors: Measures, C. I., Hatta, M.
• Format: Article
• Language: English
• Subjects: Abyssal zone; Aluminium; Aluminosilicates; Aluminum; Aluminum silicates; Arctic Ocean; Basins; Biological materials; Bottom water; Chemical properties; Chemical reactions; Chemicophysical properties; Concentration gradient; Continental margins; Deep water; Enrichment; Geophysics; Gradients; Ocean basins; Oceans; Remineralization; Sediment; Sediments; Signal processing; Silicic acid; Silicon; slope processes; Surface water; Tracers; Turbidity; Turbidity currents; Vertical profiles; Water circulation; Water column; Water currents; Weathering
• ISSN: 2169-9275; 2169-9291
• DOI: 10.1029/2021JC017399

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