Sediment cores were collected from the NOAA research vessel John N. Cobb in May 2000 using a Benthos gravity corer. Cores were taken in 10 silled embayments/fjords with restricted circulation or in ocean basins that may periodically become anoxic. Embayments sampled were Hawk Inlet on northwestern Admiralty Island at 58° 54.69/134° 35.821, Katlian Bay, Nakwasina Inlet, Krestof Sound, Deep Inlet, and Inner and Outer Redoubt Bay near Sitka, Alaska. Basins sampled were outer Sitka Sound, Eastern Channel (also Sitka Sound), and off the Sitka ferry terminal. Water depths at core sites ranged between 57 to 223 meters. Cores varied in length from 51 to 155 cm.

In the lab, cores were extruded when necessary, split lengthwise, and examined for sediment characteristics including laminations, presence of macrofossils, and color. Subsamples of sediment were collected downcore for analyses of organic carbon (OC), carbonate content, δ¹³C and δ¹⁵N isotope ratios, diatom and microfossil identification (smear slides), and radiocarbon dating. X-ray and magnetic susceptibility data were also collected for each core.

Mean OC ranged from 9.1 to 20.0% of dry weight. Sites with the highest OC values were Inner and Outer Redoubt Bays and Deep Inlet; Hawk Inlet had the lowest OC values. In most cores, OC changed little downcore, although four cores showed a slight decrease in OC over time. Mean carbonate content ranged from 7.1 to 41.8% of total organic carbon. Outer Redoubt Bay had the highest carbonate content and Hawk Inlet the lowest. Five cores showed a declining trend in carbonate content downcore; the rest showed varying trends.

Smear slides were made at regular sampling intervals (typically every 10 cm) from each core and scanned at 400X. Microscope scans provided information about core sediments including grain size, mineralogy, microfossil types and their relative abundance. A minimum of 100 components was identified for each slide. Organisms include diatoms, foraminiferans, silicoflagellates, and sponge spicules. Wood fragments and spores were also noted. Diatoms were the most numerous in all samples (Coscinodiscus sp. and other centrics predominating). Silicoflagellates occurred in moderate to small numbers (Distephanus sp. the most numerous). Sponge spicules were of many types and often fragmented. Siliceous versus calcareous sponges were distinguished under polarized light (siliceous sponge spicules predominate). Foraminiferans were few to very rare in these slides even at 100X scans.

Radiocarbon dating is in progress to determine the time period covered by these records. Ultimately, we hope to use this data to identify sites for high resolution paleoceanographic studies in this region.