Particulate Organic Matter and Nutrient Utilization in the Mixed Layer of the Ross Sea

Abstract

The relationship between particulate organic matter, nutrient depletion and vertical stability were studied in different areas of the Ross Sea during the Antarctic spring and summer. In the upper mixed layer, identified in relation to the vertical stability index E[Z(UML)], a significant relationship between the vertical stability index and nutrient depletion was found. A similar relationship was also observed between particulate matter distribution and composition vs. nutrient utilization. Data analysis showed that stations could be divided into different groups with differing characteristics. Summer stations in the western and central areas of the Ross Sea and in the coastal zone of Terra Nova Bay were affected by ice melting and showed strong stratification (E[Z(UML)] > 25), higher biomass and nutrient depletion values (average values of POC = 236 µg |-1; PON = 40 µg |-1; ΔNW, ΔPW, ΔSiW = 7, 0.7, 23 mmol m-3, respectively). Another group of stations in the northern-central area of the Ross Sea was characterized by low nutrient utilization (ΔNW, ΔPW, ΔSiW 180 µg |-1 and PON > 29 µg |-1) and with phytoplankton assemblages dominated by diatoms and/or Phaeocystis antarctica. The degree of stabilization, but also sedimentation rates and grazing pressure played an important role in the development, accumulation and spatial variability of particulate organic matter in the Ross Sea areas.