The Composition and cycling of Dissolved organic matter-i Review of DOC distribution Review of radiocarbon in DOC Sources of DOC Seasonal cycling of DOC above the permanent thermocline Composition of DOC DOC and global change DOC and major carbon reservoirs and fluxes Terrestrial Plants 900 GT C Atmosphere 750 GT (CO 2 ) Terrestrial Primary Production 50-75 GT C/yr Soil 2000 GT C Carbonates 60,000,000 GT C Kerogen 20,000,000 GT C River flux 0.5 GT C/yr Burial 0.1-0.2 GT C/yr Marine Primary Production 50-75 GT C/yr POC 15 GT C Biomass 2 GT C DOC 700 GT C 150 GT C 1
Distribution of Dissolved Organic Carbon (DOC) [DOC µm] High in surface, low in deep water Measured by high temperature combustion Surface values 60-80 µm, deep 40 µm Global inventory about 700 GT C Global circulation and the distribution of DOC 2
Global distribution of radiocarbon in DIC at 10 m DIC radiocarbon fields at 10 m contoured from WOCE data http:// cdiac.esd.ornl.gov /oceans/glodap/glopdv.htm. Highly stratified portions of gyres characterized by low horizontal advection have high values for DICΔ 14 C. Radiocarbon in the Atlantic and Pacific Oceans DIC 14 C in surface waters of the Atlantic and Pacific has the same isotopic value. DOC is always older than DIC (by 4 kyrs in surface water) ΔΔ 14 C of DIC and DOC is about the same in the deep Atlantic and Pacific Deep ocean values of DOC are equal to a radiocarbon age of 4-6 kyrs Annual flux = 0.1 GT C yr -1 Either there is a source of old DOC, or DOC persists for several ocean mixing cycles 3
Δ 14 C= reactive DOC + nonreactive DOC Atlantic surface water 14 C calc = -120 14 C obs = -127 nonreactive DOC Δ 14 C = DOC (deep) reactive DOC Δ 14 C=DIC Modern (< 50 yr?) Pacific surface water 14 C calc = -147 14 C obs = -148 Nonreactive DOC = 650 GT C Reactive DOC = 30-50 GT C The radiocarbon value of DIC is currently decreasing by 4 yr -1 The reactive fraction of DOC has a T r of <3 yr? 200 150 100 50 0-50 DIC 1 year 2 years 3.3 years 10 years -100 1952 1962 1972 1982 1992 2002 year 4
Reactivity and the cycling of DOC in seawater reactive DOC Δ 14 C=? Nonreactive DOC Δ 14 C = DOC (deep) Very reactive DOC Δ 14 C=DIC Heterotrophic microbial production?? 0 o and 140 o W Carlson and Ducklow, DSR II v 42; 639-656 Reactivity and the cycling of DOC in seawater Nonreactive DOC Δ 14 C = DOC (deep) reactive DOC Δ 14 C=? Annual production of DOC is much higher than suggested by RC flux measurements of the nonreactive reservoir alone Very reactive DOC Δ 14 C=DIC Heterotrophic microbial production?? 0 o and 140 o W Carlson and Ducklow, DSR II v 42; 639-656 5
Reactivity and the cycling of DOC in seawater Nonreactive DOC Δ 14 C = DOC (deep) reactive DOC Δ 14 C=? Annual production of DOC is much higher than suggested by RC flux measurements of the nonreactive reservoir alone Very reactive DOC Δ 14 C=DIC What is the annual flux of DOC? How important is it to the marine C cycle? What is DOC? Heterotrophic microbial production?? Why does it accumulate? 0 o and 140 o W Carlson and Ducklow, DSR II v 42; 639-656 What are the sources of DOC? Atmospheric input of DOC [DOC µm] marine production, &/or rivers sediments 6
What are the sources of DOC? Atmospheric input of DOC [DOC µm] Input of DOC from rivers = 0.4 GT C/yr, which is enough to drive the marine DOC cycle. marine production, or rivers sediments What are the sources of DOC? Atmospheric input of DOC [DOC µm] Stable carbon ( 13 C) isotopes suggest a marine source marine production, or rivers sediments δ 13 C 7
Production of DOC by phytoplankton in axenic laboratory culture* Mague et al. L&O v 25 (1980) Production of DOC by phytoplankton in axenic laboratory culture* Mague et al. L&O v 25 (1980) 8
What are the sources of DOC? Release of DOC from marine sediments Burdige et al, GCA 1994 & 1999 What are the sources of DOC? Burdige et al, GCA 1994 & 1999 9
What are the sources of DOC? Sediments are a source for DOC- sediment pore-water concentrations of C are higher than seawater, and there is a flux out of sediments into the water column. Only a few measurements have been made, and the global flux is estimated to be small, but on the order of what is needed to maintain DOC stocks. Burdige et al, GCA 1994 & 1999 What are the sinks for DOC in seawater? reactive DOC Δ 14 C=? Nonreactive DOC Δ 14 C = DOC (deep) Very reactive DOC Δ 14 C=DIC Heterotrophic microbial production?? 0 o and 140 o W Carlson and Ducklow, DSR II v 42; 639-656 10
Annual cycle of DOC production in the mixed layer at BATS* *Bermuda Atlantic Time Series, a JGOFs LTEM site Carlson et al.1994; Nature Depth (m) 100 200 300 400 500 35 45 55 65 75 0 Seasonal Variability of DOC distribution in the Ross Sea DOC (µm C) 35 45 55 65 75 35 45 55 65 75 35 45 55 65 75 600 Late winter Spring Summer Late Fall 700 800 AESOPS PI RSPP 94 AESOPS PIV RSPP 95 AESOPS PII AESOPS PIII Carlson and Hansell 2003 11
BATS DOC (µm C) Hansell and Carlson In situ measurements of DOC suggest production/degradation timescales of 1-3 months (seasonal). Can we experimentally show this? 72 DOC (µm C) 67 ML t-0 4-7 days Month 62 Oct 92 July 93 July 97 Aug 97 Sept 97 April 98 Aug 98 July 99Aug 2001 Data from Craig Carlson 12
In situ measurements of DOC suggest production/degradation timescales of 1-3 months (seasonal). Can we experimentally show this? 72 DOC (µm C) 67 ML t-0 4-7 days Month 62 Oct 92 July 93 July 97 Aug 97 Sept 97 April 98 Aug 98 July 99Aug 2001 Could this be the result of NUTRIENT LIMITATION? or is the DOM INTRINSICALLY NON-LABILE? Data from Craig Carlson Accumulation of DOC in the euphotic zone does not appear to be a problem of nutrient limitation 72 With some macro nutrients added: N (1µM) P (0.1 µm ) 67 62 7/97 N 7/97 P 7/97 N,P 8/97 N 8/97 P 9/97 N,P 4/98 N,P 8/98 N,P ML t-0 4-7 days Month Data from Craig Carlson 13
Accumulation of DOC in the euphotic zone does not appear To be a problem of nutrient limitation 72 With some macro nutrients added: N (1µM) P (0.1 µm ) 67 62 7/97 N 7/97 P 7/97 N,P 8/97 N 8/97 P 9/97 N,P 4/98 N,P 8/98 N,P ML t-0 4-7 days Month From microbial degradation experiments, nutrient Limitation does not appear to be the major factor Leading to DOM accumulation in the euphotic zone. Is DOM intrinsically non-labile? Data from Craig Carlson 14