|DOM in the deep Atlantic Ocean|
Dissolved organic matter (DOM) in the deep ocean is one of the largest reservoirs of reduced carbon on Earth. Taken as a bulk pool, this material is dilute and highly degraded, residing in the deep ocean for thousands of years. From a molecular standpoint, however, there are many sources of deep ocean DOM that may have unique and trace-able signatures. Specifically, refractory DOM is transported laterally with large water mass movement; semi-labile DOM is delivered through vertical mixing and particle degradation; and labile DOM could be produced in situ by free-living and attached microbes. The overall balance of these processes determines the composition of deep-water DOM but the temporal and spatial variations in this balance are unknown. Since the role of DOM in the marine carbon cycle is determined by the reactivity and/or production of different molecules within this complex mixture, bulk DOM concentrations and isotopic compositions are insufficient to elucidate the molecular-level processes at work in this environment. Consequently, we propose to examine the molecular-level composition of deep ocean DOM along a north-south transect of the Atlantic Ocean where we can sample three major deep-water masses: North Atlantic Deep Water (NADW), Antarctic Bottom Water (AABW) and Antarctic Intermediate Water (AAIW). With ultrahigh resolution mass spectrometry and multi-stage fragmentation coupled to liquid chromatography, we plan to assess DOM composition along the paths of these water masses and to offer structural clues to refractory and labile components of DOM. With quantitative mass spectrometry, we will provide estimates for temporal and spatial variability in new marker compounds. Together, these results will provide fundamental information needed to understand the spatial and temporal dynamics of deep ocean DOM as a critical component of the global carbon cycle.
The proposed project will examine the following two hypotheses:
- Hypothesis 1: The molecular-level composition of marine DOM will vary vertically and horizontally as a function of environmental transport processes
We will use ultrahigh resolution mass spectrometry to assess the composition of DOM in the western Atlantic Ocean. We will follow the southward trajectory of NADW along the eastern coast of North America, through the region of intersection with northward-flowing AAIW and AABW. Along this path, we will examine the impact of source water, transport and surface processes on DOM composition.
- Hypothesis 2: There will be changes in the relative concentration of marker compounds within DOM as water masses move in the deep ocean
Our planned 8000 km cruise track incorporates repeated sampling of NADW, AAIW and AABW. We will use ultrahigh resolution mass spectrometry and multivariate statistical tools to identify compounds that are unique to each water mass, multistage fragmentation to discern their structure, and quantitative mass spectrometry to examine the temporal and spatial variability of these compounds. We will compare the dynamics of the unique marker compounds relative to refractory compounds in order to elucidate factors underlying carbon transport and storage in the deep ocean.
Funding: WHOI Deep Ocean Exploration Institution (2010-12), NSF Chemical Oceanography (2012-15; OCE-1154320); Personnel: Krista Longnecker (Research specialist / lab manager), Winn Johnson (JP student).
Publications: None yet.