Late Holocene radiocarbon variability in Northwest Atlantic slope waters

Deep-sea gorgonian corals secrete a 2-part skeleton of calcite, derived from dissolved inorganic carbon at depth. and gorgonin, derived from recently fixed and exported particulate organic matter. Radiocarbon contents of the calcite and gorgonin provide direct measures of seawater radiocarbon at depth and in the overlying surface waters, respectively. Using specimens collected from Northwest Atlantic slope waters, we generated radiocarbon records for surface and upper intermediate water layers spanning the pre- and post-bomb- C-14 eras. In Labrador Slope Water (LSW), convective mixing homogenizes the pre-bomb Delta C-14 signature (-67 +/- 4 parts per thousand) to at least 1000 m depth. Surface water bomb-C-14 signals were lagged and damped (peaking at similar to+45 parts per thousand in theearly 1980s) relative to other regions of the Northwest Atlantic, and intermediate water signals were damped further. Off southwest Nova Scotia, the vertical gradient in Delta C-14 is much stronger. In surface water, pre-bomb A 14C averaged -75 +/- 5 parts per thousand. At 250-475 m depth, pre-bomb Delta C-14 oscillated quasi-decadally between -80 and -100 parts per thousand, likely reflecting interannual variability in the presence of Labrador Slope Water vs. Warm Slope Water (WSW). Finally, sublossil corals reveal no systematic changes in vertical Delta C-14 gradients over the last 1200 yr. (c) 2008 Elsevier B.V. All rights reserved.