Productivity and sedimentary delta N-15 variability for the last 17,000 years along the northern Gulf of Alaska continental slope

• Main Authors: Addison, Jason A., Finney, Bruce P., Dean, Walter E., Davies, Maureen H., Mix, Alan C., Stoner, Joseph S., Jaeger, John M.
• Format: Article in Journal/Newspaper
• Language: English; unknown
• Published: American Geophysical Union
• Subjects: Gulf of Alaska; Sea ice; Alaska
• Online Access: https://ir.library.oregonstate.edu/concern/articles/df65v9365

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⁻² kyr⁻¹) 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 δ¹⁵N ratios, indicating a link between productivity, nitrogen cycle dynamics, and sedimentary anoxia. After applying a correction for terrestrial δ¹⁵N contributions based on end-member mixing models of terrestrial and marine organic matter, the resulting B-A marine δ¹⁵N (6.3 ± 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 ...