- 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 from altered ocean/atmospheric
circulation during the B-A in the Gulf of Alaska.
- Addison, J. A., B. P. Finney, W. E. Dean, M. H. Davies, A. C. Mix, J. S. Stoner, and J. M. Jaeger (2012), Productivity and sedimentary δ¹⁵N variability for the last 17,000 years along the northern Gulf of Alaska continental slope, Paleoceanography, 27, PA1206, doi:10.1029/2011PA002161.
- The published article can be found at AGU - American Geophysical Union.
|Funding Statement (additional comments about funding)
- This publication results in part from aUAF Center for Global Change Student Award to J.A.A. funded by theCooperative Institute for Arctic Research through cooperative agreementNA17RJ1224 with the National Oceanic and Atmospheric Administration.B.P.F. was supported through NSF grant OCE-0351075. W.E.D. was supported by the USGS Earth Surface Dynamics Program.
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