High lipid composition of particulate organic matter in the northern Chukchi Sea, 2011

Abstract We investigated the biochemical compositions (lipids, proteins, and carbohydrates) of particulate organic matter (POM) as a potential food source in the northern Chukchi Sea. We aimed to understand physiological status of phytoplankton, determine important controlling factors, and estimate the energetic contents of POM. The major inorganic nutrients were generally depleted at upper mixed-layer depth (>20 m). The average chlorophyll a (chl- a ) concentration was 31.9 mg m −2 (S.D.=±31.3 mg m −2 ) in this study, significantly higher than that reported previously in the northern Chukchi Sea. Small phytoplankton (0.7–5 µm) accounted for 65.9% of total chl- a concentration. The overall average compositions of lipids, carbohydrates, and proteins were 50% (S.D.=±10.7%), 35% (S.D.=±11.0%), and 15% (S.D.=±11.2%) for POM, respectively. Along with other evidence (e.g., low N:P and protein–carbohydrate ratios), the high lipid and low protein compositions of POM in this study suggests that phytoplankton might have had a nitrogen limitation and/or stationary growth phase in the northern Chukchi Sea during the cruise period, 2011. The overall average calorific content of food material (FM) was 149.2 μg L −1 (S.D.=±36.5 μg L −1 ) or 1.0 Kcal m −3 (S.D.=±0.2 Kcal m −3 ). The relatively higher calorific contents in the northern Chukchi Sea were due to high lipid contributions and the considerably high calorific content of FM per POC.