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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).

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The short-term effects of inorganic N and P (nitrate, ammonium, phosphate) and organic C and N (glucose, amino acids) input, added separately as well as jointly, on microplankton community structure and metabolism were studied in 6 microcosm experiments conducted from February to July 2008 in a eutrophic coastal embayment in NW Spain under contrasting hydrographic conditions. The responses of planktonic communities were highly variable. Strong positive effects of combined inorganic and organic nutrient enrichments for phytoplankton and heterotrophic bacteria were found. In most experiments enhanced phytoplankton biomass and productivity (primary production increased up to 5.5-fold) was measured after mixed (inorganic plus organic) additions but phytoplankton responded only in one of the experiments after inorganic additions. Heterotrophic bacteria responded faster than phytoplankton to the additions but were never affected by inorganic nutrient additions, suggesting a C limitation of bacterial activity in this coastal environment. Heterotrophic bacteria biomass, productivity, and respiration responded to mixed additions (containing C, N, and P) in all the experiments (bacterial production increased from 14-to 34-fold) whereas its response to organic (containing C and N) additions greatly differed among experiments (bacterial production increased from 0.6-to 21-fold), which could be partially related to P availability. A general increase in bacterial growth efficiency occurred only after mixed additions (up to 2-fold). The tendency towards heterotrophy of the microbial plankton community was weaker after the mixed (Production/Respiration (P/R) ratio changes from 0.34-to 1.6-fold) than after the organic additions (P/R changes from 0.16-to 0.8-fold). Our results suggest that phytoplankton requirememnts for organic nutrients for growth and P deficiency of bacterial populations intermittently occur in this coastal area. KEY WORDS: Nutrient additions · Organic nitrogen · Phytoplankton · BacteriaResale or republication not permitted without written consent of the publisher

Temperate, transitional and subtropical waters of the remote Azores Front region east of Azores (24-40ºN, 22-32ºW) were sampled during three cruises conducted under increasing stratification conditions (April 1999, May 1997 and August 1998 respectively. Vertical eddy diffusion is 35% and 2% of the spring and summer sinking POC flux, respectively. On the other hand, DOC only contributes 13% to the local oxidation of organic matter in subsurface waters (between the pycnocline and 500m) of the study region.

fluxes through the Strait of Gibraltar and estimated a revised nitrogen excess rate of 22 ± 19 × 10 10 mol N y 1. The average volumetric rate of N 2 fixation for this zone was only 1.3 × 10 3 nmol N L 1 d 1 , indicating that its influence in Pnew and nitrogen excess production in this part of the Atlantic is negligible.

[1] The average composition of the dissolved and particulate products of early degradation of marine phytoplankton has been established for the first time in a coastal upwelling system using a mixing analysis along isopycnal surfaces combined with a stoichiometric model. About 17-18% of the mineralized organic matter is derived from the decomposition of organic particulates, and 16-35% is from the dissolved organic matter. The remaining 50-70% is derived probably from large fast sinking particles. On average, the mineralized material on large particles has the closest composition to the Redfield formula. The ratio of dissolved saccharides to dissolved organic matter respiration is >40% higher than expected from a material of Redfield composition. Finally, the ratio of lipid to particulate organic matter respiration is >80% larger than expected from a material of Redfield composition. Regarding the decomposition of hard structures, biogenic silica dissolves predominantly in the inner shelf, where organic carbon oxidation is more intense, and diatom deposition occurs preferentially.