Abstract
Here, I utilize dissolved organic carbon (DOC) as a qualitative indicator for localized particle export to better understand three major processes that stimulate primary production and subsequent deep, DOC-releasing particle export. First, I discuss evidence that a significant export event in the subarctic North Pacific in spring 2018 was a result of an anomalous bloom of gelatinous zooplankton. I further quantify the seasonality and interannual variability of deep organic carbon concentrations to better understand the temporal limitations of DOC as a proxy for deep export. Second, I present unique evidence of deep export beneath prominent fronts in the transitional region between the subarctic and subtropical gyres of the North Pacific. A further discussion is presented on the interdependence of front-associated export and the local biogeochemical dynamics, such as relative depths of the nutricline, mixed layer shoaling, and seasonal intersections of the two. In the third chapter, I present two stark distributions of bathypelagic DOC measured a decade apart (2008 vs. 2017) along the same transect in the Southern Ocean. A discussion ensues on the dependency of deep, DOC-releasing export and iron influx from two major sources: nutrient injection from depth and iron associated with sea ice melt during a major, anomalous ice melt event. The relative balance of these influxes appeared to influence the differences in the two DOC profiles.
This work also illuminates the value of employing anomalous enhancements of DOC concentrations in the deep ocean as a proxy for the recent presence of particulate matter. Particles are fleeting in nature due to the variety of temporal and spatial processes that occur during their production and descent, which cause the direct observation and quantification of particle export to be quite challenging. The evidence provided here demonstrates the value of utilizing anomalous enhancements of DOC concentrations in the deep ocean as a proxy for export, in hopes that the scientific community acknowledges and further explores the value of these DOC signatures.