Does Copepod Grazing Control Large Phytoplankton in the HNLC Region of the Southern Ocean?

95-30819 Dagg本研究项目是美国联合全球海洋通量研究(JGOFS)南大洋计划的一部分，旨在(1)更好地了解南大洋有机和无机碳的通量，(2)确定调节这些通量的大小和变化的物理、生态和生物地球化学因素和过程，以及(3)将这些通量置于当代全球碳循环的背景下。大型浮游植物，特别是硅藻，通常在包括南极极地前沿带(APFZ)在内的南大洋永久无冰区域生长缓慢，原因是微量营养素(Fe)限制或与深层混合有关的光限制或限制。据推测，在这些条件下，大型浮游植物的生长大致是通过从桡足类群落中摄食来平衡的。当铁输入或改善光照条件促进大型浮游植物的生长时，假设额外的生长主要被桡足类群落的功能反应所吸收。然而，浮游植物生长的较大促进将饱和对硅藻的捕食增加了沉降物的硅：碳比，因为大约70%的摄取的碳被桡足类的肠壁同化，而硅是消化惰性的。这些关系将通过船上实验来解决，这些实验旨在测量大型桡足类动物对APFZ大型浮游植物的摄食率，并通过测量桡足类粪便颗粒和沉积物捕集器材料中碳与生物硅的比率来解决这些关系。

95-30819 DAGG This research project is part of the US Joint Global Ocean Flux Study (JGOFS) Southern Ocean Program aimed at (1 ) a better understanding of the fluxes of carbon, both organic and inorganic, in the Southern Ocean, (2) identifying the physical, ecological and biogeochemical factors and processes which regulate the magnitude and variability of these fluxes, and (3) placing these fluxes into the context of the contemporary global carbon cycle. Large phytoplankton, especially diatoms, typically grow slowly in the permanently ice-free regions of the Southern Ocean, including the Antarctic Polar Front Zone (APFZ), because of micronutrient (Fe) limitation or light limitation or limitation associated with deep mixing. It is hypothesized that under these conditions the growth of large phytoplankton is approximately balanced by grazing from the copepod community. When growth of large phytoplankton is enhanced by Fe inputs or improved light conditions, it is hypothesized that the additional growth is mostly absorbed by the functional response of the copepod community. Larger enhancements of phytoplankton growth however, will saturate the grazing on diatoms increases the Si:C ratio of sinking matter because approximately 70% of ingested carbon is assimilated across the copepod gut wall but Si is digestively inert. These relationships will be addressed by shipboard experiments designed to measure the feeding rates of large copepods on large phytoplankton of the APFZ, and by measurements of the ratio of carbon to biogenic silica in copepod fecal pellets and in sediment trap materials.