Water mass age and aging driving chromophoric dissolved organic matter in the dark global ocean

Abstract

The omnipresence of chromophoric dissolved organic matter (CDOM) in the open ocean enables its use as a tracer for biochemical processes throughout the global overturning circulation. We made an inventory of CDOM optical properties, ideal water age (τ), and apparent oxygen utilization (AOU) along the Atlantic, Indian, and Pacific Ocean waters sampled during the Malaspina 2010 expedition. A water mass analysis was applied to obtain intrinsic, hereinafter archetypal, values of τ, AOU, oxygen utilization rate (OUR), and CDOM absorption coefficients, spectral slopes and quantum yield for each one of the 22 water types intercepted during this circumnavigation. Archetypal values of AOU and OUR have been used to trace the differential influence of water mass aging and aging rates, respectively, on CDOM variables. Whereas the absorption coefficient at 325 nm (a 325 ) and the fluorescence quantum yield at 340 nm (Φ 340 ) increased, the spectral slope over the wavelength range 275-295 nm (S 275-295 ) and the ratio of spectral slopes over the ranges 275-295 nm and 350-400 nm (S R ) decreased significantly with water mass aging (AOU). Combination of the slope of the linear regression between archetypal AOU and a 325 with the estimated global OUR allowed us to obtain a CDOM turnover time of 634 ± 120 years, which exceeds the flushing time of the dark ocean (>200 m) by 46%. This positive relationship supports the assumption of in situ production and accumulation of CDOM as a by-product of microbial metabolism as water masses turn older. Furthermore, our data evidence that global-scale CDOM quantity (a 325 ) is more dependent on aging (AOU), whereas CDOM quality (S 275-295 , S R , Φ 340 ) is more dependent on aging rate (OUR).

Photochemical Mineralization of Terrigenous DOC to Dissolved Inorganic Carbon in Ocean

“…In the ocean, microbial metabolism is often considered to be as a source rather than a sink of CDOM [Jørgensen et al, 2014]. In the deep dark ocean, the estimated turnover time of CDOM is 634 years [Catalá et al, 2015], indicating very slow biobleaching rates. Thus, it is not always clear whether microbial metabolism is a sink or a source of tCDOM in marine waters, but it is likely that microbes biobleach tCDOM when they consume non-labile tDOC rich in tCDOM Wetzel , 2004, 2008;Koehler et al, 2012].…”

Drivers of fluorescent dissolved organic matter in the global epipelagic ocean

“…A portion of CDOM is also able to emit fluorescence when excited by light and it was termed fluorescent dissolved organic matter (FDOM) (Kalle ). Recently, the spectroscopic properties of DOM have allowed tracing long‐term biogeochemical processes in the global ocean (e.g., Jørgensen et al ; Nelson and Siegel ; Catalá et al ; Stedmon and Nelson ). Excitation emission matrices (EEMs) consisting of a series of fluorescence emission spectra collected across a range of excitation wavelengths is the most common tool used to characterise FDOM in aquatic environments.…”

The Benthic Megafaunal Assemblages of the CCZ (Eastern Pacific) and an Approach to their Management in the Face of Threatened Anthropogenic Impacts

“…This ocean region, associated with the highly productive equatorial upwelling to the east, is identified as the North Pacific Tropical Gyre province (NPTG) (Longhurst, 2007 (Catalá et al, 2015a,b) (Figure 8). The thermohaline and intermediate waters (500-1,500 m) in the CCZ present unique features as they undergo excessive aging (Catalá et al, 2015b). This anomaly is associated with (1) the high biological productivity of the area, which exports organic material from the surface to the deep ocean (Feely et al, 2004), and (2) the sluggish circulation of the North Pacific that facilitates organic matter sinking.…”