DOI: 10.25921/nce7-wt65
title: NOAA/WDS Paleoclimatology - Gulf of Alaska 17,000 Year Paleoproductivity Data

description: 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 glaciomarine 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 d15N ratios, indicating a link between productivity, nitrogen cycle dynamics, and sedimentary anoxia. After applying a correction for terrestrial d15N contributions based on end-member mixing models of terrestrial and marine organic matter, the resulting B-A marine d15N (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.
description: Multiproxy sediment paleoproductivity data from a jumbo piston core collected on the northern Gulf of Alaska continental slope. Proxy data measured include biogenic opal, organic carbon, organic matter stable isotopes, and trace metal data. 

These organic and inorganic geochemical data are from the northern continental slope of the Gulf of Alaska, and span from 1.1 to 17.4 calibrated kyrs ago.  This marine sediment record is continuous and well-dated by 37 AMS radiocarbon dates on planktonic foraminifera (see Davies et al., 2011 for further information). 

Opal was measured by a 0.1 M NaCO3 extraction and a molybdate-blue spectrophotometric method (Mortlock and Froehlich, 1989). Total organic carbon (TOC) and total nitrogen (TN) were measured on a carbonate-free subsample by combustion in a Costech 4010 HCNS elemental analyzer.  Organic matter d13C and sedimentary d15N were measured on a carbonate-free subsample using a Finnigan Delta-plus XP isotope ratio mass spectrometer.  CaCO3 data is a combination of total Ca measured by ICP-OES (n = 110), calibrated with a smaller number of CaCO3 coulometric measurements (n = 43).  Inorganic element concentrations (Al, Mn, Co, Cr, U, Mo, and Cd) were measured by a combination of ICP-OES and ICP-MS at SGS Minerals Services in Toronto, Canada. 

A terrestrial-N-corrected dataset of sedimentary d15N is also included. This data reflects the application of a linear endmember mixing model between terrestrial and marine organic matter to remove the influence of terrestrial N from the bulk sedimentary d15N measurements. These data should be considered on a qualitative basis only. Please see Addison et al. (2012) or contact the author directly for further information. 

Core EW0408-85JC: 59°33.3'N, 144°9.21'W, 682 m water depth