Chlorophyll a in Arctic sediments implies long persistence of algal pigments

Sediment cores were collected from the shelf, slope, and basin of the Bering, Chukchi, and Beaufort Seas during May–June (under ice cover) and July–August (largely ice-free) 2004. Measurements of chlorophyll a (chl a), total organic carbon (TOC), and C/N ratios were made in surface and some subsurface core increments. Surface sediment chl a decreased with increasing water depth. Significant positive correlations were found between chl a and TOC and chl a and C/N ratios in the basin (>2000 m), but there were significant negative correlations between chl a and C/N ratios on the shelf (⩽200 m). Chl a values generally declined in down-core profiles, but in some deeper slope and basin cores, measurable inventories of subsurface chl a were present at depth. In some cases, these subsurface chlorophyll inventories coincident with peak activities of the anthropogenic radionuclide 137Cs were detected, which had maximal deposition following the atmospheric nuclear weapons testing era in the 1960s. A sedimentation rate independently determined for one of these cores using 210Pb was consistent with the depths of subsurface 137Cs peaks in slope sediments reflecting steady, relatively undisturbed deposition over a several-decade period. The depth of penetration of 137Cs in some continental slope sediments, together with detectable chl a, suggests that chl a can be buried in some of these deeper-water sediments under cold conditions for decadal periods in the absence of deposit feeders. Because organic deposition from the water column is episodic at high latitudes and concentrated following the spring bloom, these buried sources of organic materials, whether on the shelf or in deeper basin sediments, may ultimately be important for benthic invertebrates that could utilize this food source during times of the year when primary production flux from the overlying water column is reduced.