Biological processes in the mesopelagic zone of the North Pacific: active carbon transport

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A significant challenge for marine ecologists is to be able to predict climate change impacts, including acidification, warming and oxygen decline, on marine, particularly deep-sea, pelagic ecosystems. Biological removal of carbon from the upper, euphotic zone and export to the deeper waters, called the biological pump, plays a variable but significant role in determining carbon dioxide exchange at the surface. Greater than 90% of the organic matter exported both passively and actively from the euphotic zone is remineralized within the mesopelagic layer, which extends from the bottom of the euphotic zone (~ 100 m) to depths greater than 1000 m. Some of this material is returned to the surface as nutrients, microelements and carbon dioxide on decadal scales or less, while the remaining organic material is transferred to the deep ocean interior and stored for millennia. Despite importance and vastness, the mesopelagic realm is among the least studied regions of the ocean and thus our ability to predict the processes driving exchange in carbon dioxide and nutrients between the euphotic zone, deep-ocean and ocean margins is limited. The long-term goal of proposed research is to develop a broad understanding of the fundamental ecological principles driving the composition, diversity, density and stability of the mesopelagic plankton and micronekton in the ocean. We would like to identify the diss-/similarities in the structure and carbon cycling of mesopelagic zones in polar, temperate and tropical regions; second, to build an ecosystem model (future collaborative effort) that provides mechanistic links between epipelagic-mesopelagic-bathypelagic realms. The short term goals of the proposed study with the spatial focus on the NE Pacific mesopelagic zone will (a) contribute to a characterization of the composition and vertical structure of mesopelagic plankton and micronekton in the eastern temperate and sub-Arctic Pacific; (b) link structure and diversity of mesopelagic food webs to overlaying productivity, as well as to subsurface oxygen concentrations; (c) quantify the total carbon active transport from surface layers into midwaters by different groups of micronekton; and (d) assess quantitatively the “cryptic food web”. This will be built upon research opportunities provided by the long-standing monitoring programs off the west coast of Vancouver Island and at the Station Papa (western sub-Arctic Pacific). The proposed research will be important to global fisheries if midwater realm will become targeted for the future harvest. Broadly, it will be used in a collaborative effort to develop a coupled biophysical/fishery model of North Pacific. By providing novel information on midwater food webs, this proposal will lay foundation to the development of an interdisciplinary, multinational initiative to understand the mesopelagic ecosystem and its role in the marine carbon cycle as well to develop ecosystem-based management in the open ocean.