DOC, DON, DOP Cycling and Composition 4

NMR and carbohydrate analyses of deep sea HMWDOC monosaccharide distribution relative % surface relative % 5200m NMR and carbohydrate analyses of deep sea HMWDOC 13C- and 1HNMR of HMWDOC from deep samples in the Atlantic and Pacific Oceans appear to be very similar, suggesting similar composition throughout the deep ocean [DOC] can vary in space and time in the ocean due to changes in DOC production Production of DOC by phytoplankton in laboratory culture Production of DOC during grazing by macrozooplankton DOC dynamics in a simulated algal bloom Most DOC accumulation occurs after nutrients are exhausted (bloom crashes) During early log phase growth DOC is being respired by bacteria Two pools of DOC, reactive and non reactive (timescale of exp!). Are they being produced by two different classes of microbes? Production of reactive and non reactive DOC by phytoplankton and bacteria CO2 DOCr O2 DOCnr DOCnr Bacterial production is thought to be fuelled by very reactive DOC that has a residence time in seawater of hour to days. DOC cycling and bacterial production in the ocean DOC is the presumed substrate that supports bacterial metabolism in seawater. There are three “types” of DOC that Occur in seawater: Very reactive DOC- supports bacterial Production Reactive DOC that is produced and Accumulates in surface seawater. Lost During convective mixing. Non reactive DOC (most DOC) Bacterial production and Bacterial Carbon demand Bacteria are believed to be the principal sink for DOC in seawater. DOC fuels free-living bacterial production (BP) of biomass It is assumed that bacteria can out compete phytoplankton for nutrients, and that bacteria are substrate (C) limited. Bacterial production is most often measured by changes in cell #s in a sample over time, or the uptake of 3H-leucine to measure protein synthesis or 3H-thymidine to measure nucleic acid synthesis. Current estimates of global bacterial production have a wide range of values, but a mean of about 15% PP. Bacterial production is the product of bacterial carbon demand (BCD) and efficiency. Estimates of bacterial efficiency also vary from About 10-50%. Therefore BCD may be 30-50% of PP. Is there enough production of DOC to support BCD? Annual primary prod @ 70GT C yr-1 Estimates of DOC production and how this C is partitioned vary widely: Annual cycle of DOC production at BATS* *Bermuda Atlantic Time Series, a JGOFs LTEM site Estimates of Net DOC Production Based on Regional Estimates of New Production for Component Regions of the World's Oceans Region Tropical open ocean - Upwelling - Turbulent mixing Southern Ocean Subarctic gyres Coastal upwelling Monsoonal Subtropical gyre Continental margins - Western boundary currents - Estuarine influenced shelves Total ∆DOC:NP Net DOC Production, Pg C yr-1 1.5 (21) 0.7 (9.5) 0.2 0.1 0.3 (24.6) 0.07 (5.7) 1.1 (15.5) 0.3 (4) 0.8 (11) 0.4 (5.5) 0.5 (7) 0.12 0.15 0.2 0.2 0.1 0.13 (10.8) 0.04 (3.7) 0.16 (13.1) 0.08 (6.6) 0.05 (4.1) 0.7 (9.5) 0.2 0.14 (11.5) 1.2 (17) 0.2 0.24 (19.7) New Production, Pg C yr-1 7.2 1.2 The ratios of net DOC production to new production (∆DOC:NP) have been taken from the analyses presented in this paper, and from assumptions listed in the text. Values in parentheses represent percentages of the global estimate. Production of “semi”-reactive DOC by phytoplankton in culture Is the composition of accumulating DOC similar to DOC in seawater? Do phytoplankton produce semi-reactive DOC? 1HNMR In culture, phytoplankton release a large amount of DOC. The composition of this DOC does not look like DOC in seawater however (left). After bacterial degradation, labile DOC is removed leaving the semi-labile material behind. of seawater After filtration U Ga ARX G 8 7 6 5 4 3 2 1 ARX 0 8 7 6 G Ga U 8 7 6 5 4 3 2 1 Chemical shift (p.p.m.) After 37 day of degradation 0 5 4 3 2 1 0 Mol (%) 60 Initial DCNS in Enriched mesocosm (Fraction A) 50 Labile DCNS in Enriched mesocosm (Fraction D) 40 Final DCNS in Enriched mesocosm (Fraction B) Semilabile DCNS in Enriched mesocosm (Fraction E) 30 20 10 0 Fucose Rhamnose Arabinose Galactose Glucose 50 Mannose + Xylose Initial DCNS in Unenriched mesocosm (Fraction A) 40 Labile DCNS in Unenriched mesocosm (Fraction C) Mol (%) Final DCNS in Unenriched mesocosm (Fraction B) 30 20 10 0 Fucose Rhamnose Arabinose Galactose Neutral sugar Glucose Mannose + Xylose Radiocarbon model of DOC cycling Old DOC D14C = DOC(deep) New DOC D14C=DIC Changes in the semi-reactive DOC-14C value with residence time As the difference between DOC(sr) and DIC residence time increases the difference in RC age will increase as well due to non-steady model state conditions in upper oceanradiocarbon 14C. 200 del14C values 150 100 50 DIC 1 year 2 years 0 3.3 years 10 years -50 -100 1952 1962 1972 1982 year 1992 2002 Radiocarbon analyses of HMWDOC carbohydrates Sample Hawaii NPSG DIC 72+7‰(n=4) 89+7‰ Glucose Galactose Mannose Xylose Arabinose Fucose Rhamnose 47, 58 67 65 52, 58 63 49, 52 40, 57 79 103 99 94 ND 69 57 Average 56+6‰ 89+13‰ Purification of a modern carbohydrate fraction from HMWDOC also isolates an older “humic” like fraction for chemical and isotopic analyses. The “humic” fraction isolated from surface seawater. D14C = -416‰ HMWDOC from the deep sea D14C = -380 to -440 ‰ How is nonreactive DOC removed from the ocean? Photo-oxidation of CDOM Generally noted that DOC in surface waters is not colored However, deep sea DOC is colored and has fluorescence Does sunlight bleach DOC in surface water? Is this the mechanism by which non-reactive DOC is removed from the ocean? Ultrafiltration of 4000m NPSG water UF of deep sea DOC Production of LMW highly oxidized DOC with depth in the ocean DOC + hv --->> LMW photo-oxidation products DOC + Hv -->> LMW carbonyls (C=O) C=O + Uvtag --->> HPLC Not produced in dark controls,but are produced in sterile controls Highly oxidized LMW compounds are produced every Day in seawater by photo-oxidation. They serve as a substrate For bacteria and therefore a sink for non-reactive DOC light Removal of DOC by adsorption onto POC Why does suspended POC age so much with depth? Summary Isotopic evidence suggests that the large inventory of DOCi in seawater is synthesized in-situ by phytoplankton or bacteria In culture, phytoplankton release about 10% of total PP as DOC. Most of this DOC is considered to be very reactive and is metabolized by bacteria in a few days, but some persists Global estimates of bacterial carbon demand require a large Fraction of PP is funneled though DOC to bacteria (> 10%) The reservoir of DOC that accumulates in the upper ocean is Not thought to fuel BP by some, but RC data suggests otherwise Non reactive DOC is removed by photo-oxidation, and perhaps By adsorption onto sinking particles