Dissolved Organic Matter distribution, reactivity, and composition

2013 CMORE Agouron Repeta Lecture 1 Typical 1D profile of dissolved organic carbon in the ocean TOC (µM) Often measured as TOC Surface values typically 60-80 µM Deep water values @ 40 µM (implies some unknown feedback/ control of DOC values) Global inventory about 660 GT C Data from Peltzer and Hayward (1996) DSR 2013 CMORE Agouron Repeta Lecture 1

2013 CMORE Agouron Repeta Lecture 1 Global Dissolved Organic carbon (< 30 m) Hansell et al., GBC 2012 2013 CMORE Agouron Repeta Lecture 1

2013 CMORE Agouron Repeta Lecture 1 Atlantic A16 Pacific P P16 2013 CMORE Agouron Repeta Lecture 1 From Dennis Hansell CLIVAR data set

2013 CMORE Agouron Repeta Lecture 1 http://www.global-greenhouse-warming.com/images/thermohaline.jpg 2013 CMORE Agouron Repeta Lecture 1

2013 CMORE Agouron Repeta Lecture 1 Global circulation and the distribution of DOC Hansell et al. Oceanography 2009 On a global scale, carbon is sensitive to water mass transport. See it very clearly in the N Atlantic where NADW formation can be seen N of 40oN, and we can see loss of DOC in the deep pacific. Assuming steady state, then there is a 30% loss of carbon between the deep basins, and a lot of that loss occurs in Pacific north of the equator. This is interesting bc of the radiocarbon age of DOC is very old- some deep process can remove old radiocarbon. 2013 CMORE Agouron Repeta Lecture 1 6

2013 CMORE Agouron Repeta Lecture 1 How do we measure carbon fluxes in DOC ? We can measure processes that cycle carbon through DOC on very short time scales using bacterial production and carbon demand measuremetns, and over longer timescales by following the changes in DOC concentration along isopycnal surfaces. But we can also use natural abundance radiocarnon, as a built in clock. Radiocarbon is produced by spallation reactions, the collision of cosmic rays (high energy protons and neutrons from outside the solar system, produced by supernova) with N-14. A neutron collides with N-14 and ejects a proton, making C-14. The atmospheric carbon is about 1 ppt of C-14. When radiocarbon decays it ejects an electron and returns to N-14. beta decay. Half life of about 5730 year. Most C-14 is produced at an altitude of 10-15 km above the surface. Rate of synthesis depends on geomagnetic field, and cosmic ray flux. Latitudinally dependand. 2013 CMORE Agouron Repeta Lecture 1

National Ocean Sciences Accelerator Mass Spectrometry (NOSAMS) C-14 tracer measurements use >106x more C-14 than natural abundance!!!!! 2013 CMORE Agouron Repeta Lecture 1

2013 CMORE Agouron Repeta Lecture 1 History of radiocarbon in the atmosphere and ocean McNichol and Aluwihare, Chem Rev. 2007 2013 CMORE Agouron Repeta Lecture 1

2013 CMORE Agouron Repeta Lecture 1 Top “pre bomb” 14C distribution as calculated from GEOSECS alkalinity data. Bottom, measured 14C activity by GEOSECS in the 1970s. Based on these pictures, what would you predict the DOC in the deep ocean to be? 2013 CMORE Agouron Repeta Lecture 1 McNichol and Aluwihare 2007

2013 CMORE Agouron Repeta Lecture 1 DOC cycling via DO14C UV photooxidation Deep water DIC values are 800-1000 years (Craig et al.) Depth 14C(‰) Age 1880m -351 ‰ -3470+330 ybp 1920m -341 ‰ -3350+300 ybp Williams, Oeschger, and Kinney; Nature v224 (1969) 2013 CMORE Agouron Repeta Lecture 1

Peter M. Williams and Ellen Druffel; Radiocarbon in the Atlantic and Pacific Oceans Peter M. Williams and Ellen Druffel; Nature 1987, JGR 1992

Radiocarbon in the Atlantic and Pacific Oceans Sargasso suspended POC Pacific suspended POC Pacific sinking POC

Radiocarbon in the Atlantic and Pacific Oceans DIC 14C in surface waters of the Atlantic and Pacific have similar isotopic values. Sargasso suspended POC Pacific suspended POC Pacific sinking POC

Radiocarbon in the Atlantic and Pacific Oceans DIC 14C in surface waters of the Atlantic and Pacific have similar isotopic values. DOC is always older than DIC (by 2-3 kyrs in surface water) DIC POC DOC Sargasso suspended POC Pacific suspended POC Pacific sinking POC Pacific suspended POC Pacific sinking POC Sargasso suspended POC

Radiocarbon in the Atlantic and Pacific Oceans DIC 14C in surface waters of the Atlantic and Pacific have similar isotopic values. DOC is always older than DIC (by 2-3 kyrs in surface water) 14C of DIC and DOC is about the same in the deep Atlantic and Pacific Sargasso suspended POC Pacific suspended POC Pacific sinking POC Pacific suspended POC Pacific sinking POC Sargasso suspended POC

Radiocarbon in the Atlantic and Pacific Oceans DIC 14C in surface waters of the Atlantic and Pacific have similar isotopic values. DOC is always older than DIC (by 2-3 kyrs in surface water) 14C 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 Either there is a source of “old” DOC, or DOC persists for several ocean mixing cycles.

Radiocarbon based models of DOC cycling in the water column Old (low radiocarbon), non-reactive DOC New, semi-reactive DOC Atlantic surface water 14Ccalc = -120 ‰ 14Cobs = -127 ‰ Pacific surface water 14Ccalc = -147 ‰ 14Cobs = -148 ‰ No microbial carbon cycling in the deep ocean??? Williams and Druffel, 1987; Beaupre and Druffel 2009 2013 CMORE Agouron Repeta Lecture 1

Cycling of reactive and semi-labile DOC by phytoplankton and bacteria DOC”reactive” DOC”semi-labile” CO2 Heterotrophic bacteria Autotrophic microbes What DOC plots don’t show you is one of the most important aspects of DOC cycling, and that is the microbial loop. Bacterial growth and respiration is thought to be fueled by very reactive DOC that has a residence time in seawater of hour to days. 2013 CMORE Agouron Repeta Lecture 1

at best very slow removal of DOM in the deep sea Under this perspective, DOM is produced and rendered recalcitrant by marine microbes. Combined with the two component model of radiocarbon and deep sea DOC, it suggests no or at best very slow removal of DOM in the deep sea 2013 CMORE Agouron Repeta Lecture 1

LIW Depth (m) 40 mM 34 mM Very rapid degradation of DOC in the Mediterranean Sea. If DOC is refractory, why does this happen? LIW Depth (m) 40 mM 34 mM C. Sanitelli et al. 2013 2013 CMORE Agouron Repeta Lecture 1

2013 CMORE Agouron Repeta Lecture 1 Southern Ocean DOC-14 data suggests the two component model cannot be correct. 2013 CMORE Agouron Repeta Lecture 1

Could there be a transfer of carbon from the surface water into the deep ocean ? Depth [DOC] The two component model only requires a conservation of mass and isotopic abundance, but does not stipulate what the isotopic/mass distribution of DOC is within the old (deep) fraction of DOC. A number of mass/isotope mixes can constitute the old fraction of DOC. UV photooxidation Smaller amount of very old DOC, and a larger amount of younger DOC 2013 CMORE Agouron Repeta Lecture 1

2013 CMORE Agouron Repeta Lecture 1