Productivity and sedimentary δ¹⁵N variability for the last 17,000 years along the northern Gulf of Alaska continental slope

Abstract

[1] Biogenic opal, organic carbon, organic matter stable isotope, and trace metal data from a well-dated, high-resolution jumbo piston core (EW0408-85JC; 59°33.3′N, 144°9.21′W, 682 m water depth) recovered from the northern Gulf of Alaska continental slope reveal changes in productivity and nutrient utilization over the last 17,000 years. Maximum values of opal concentration ($10%) occur during the deglacial Bølling-Allerød (B-A) interval and earliest Holocene (11.2 to 10.8 cal ka BP), moderate values ($6%) occur during the Younger Dryas (13.0 to 11.2 cal ka BP) and Holocene, and minimum values ($3.5%) occur during the Late Glacial Interval (LGI). When converted to opal mass accumulation rates, the highest values ($5000 g cm À2 kyr À1 ) occur during the LGI prior to 16.7 cal ka BP, which points to a strong influence by LGI glacimarine sedimentation regimes. Similar patterns are also observed in total organic carbon and cadmium paleoproductivity proxies. Mid-Holocene peaks in the terrestrial organic matter fraction at 5.5, 4.7, 3.5, and 1.2 cal ka BP indicate periods of enhanced delivery of glaciomarine sediments by the Alaska Coastal Current. The B-A and earliest Holocene intervals are laminated, and enrichments of redox-sensitive elements suggest dysoxic-to-anoxic conditions in the water column. The laminations are also associated with mildly enriched sedimentary d 15 N ratios, indicating a link between productivity, nitrogen cycle dynamics, and sedimentary anoxia. After applying a correction for terrestrial d 15 N contributions based on end-member mixing models of terrestrial and marine organic matter, the resulting B-A marine d 15 N (6.3 AE 0.4 ‰) ratios are consistent with either mild denitrification, or increased nitrate utilization. These findings can be explained by increased micronutrient (Fe) availability during episodes of rapid rising sea level that released iron from the previously subaerial coastal plain; iron input from enhanced terrestrial runoff; and/or the intermittent presence of seasonal sea ice resulting from altered ocean/atmospheric circulation during the B-A in the Gulf of Alaska.

Integrating satellite observations and modern climate measurements with the recent sedimentary record: An example from Southeast Alaska

“…Negative Pearson correlations exist between natural‐log‐transformed values of opal and TOC ( n = 8, r = −0.90, p < 0.01), and natural‐log‐transformed values of organic δ 13 C and molar N/C ratios ( n = 8, r = −0.894, p < 0.01). Applying a linear mixing model to estimate the fraction of marine‐derived organic matter that uses a terrestrial end‐member δ 13 C composition of −26‰ and a marine end‐member δ 13 C ratio of −21‰ [ Meyers , ; McQuoid et al ., ; Walinsky et al ., ; Addison et al ., ] yields a range of marine‐derived organic matter fractions of between 0.71 and 0.93 (Figure ).…”

Dissolved gallium in the Beaufort Sea of the Western Arctic Ocean: A GEOTRACES cruise in the International Polar Year

“…Climate change, including an earlier loss of sea ice (Tremblay et al, 2006) and sea level rise (Addison et al, 2012) influencing production and denitrification in Pacific waters entering the Arctic, could result in overestimating the influence of Pacific waters due to denitrification (Jones et al, 1998). Further research is therefore warranted to investigate dissolved Ga as a complimentary tracer of Pacific waters, including sampling dissolved Ga in the Bering and Chukchi Seas, through the Canadian archipelago, and in the Eastern Arctic.…”

Data report: X-ray florescence scanning of sediment cores, Site U1419, Gulf of Alaska

“…Diamicts accumulated from the deglacial (~17.5 ka) through to ~14.8 ka, after which warming coincident with the Bølling Interstate of northern Europe and Greenland resulted in a lithofacies transition to laminated mud (Davies et al, 2011). Periods of enhanced water column productivity and bottom water hypoxia between 10.7 and 14.8 ka are recognized by this laminated facies (Addison et al, 2012). The Holocene period of accumulation consists of massive bioturbated mud (Davies et al, 2011).…”

“…F1) (see the "Site U1419" chapter [Jaeger et al, 2014b]). Previous results from the site reveal a high-resolution, heterolithic, deglacial-modern sedimentary record (Davies et al, 2011;Addison et al, 2012). The drilling objectives of Site U1419 were to extend this record of glacial dynamics and paleoceanography into the late Pleistocene.…”