CO 2. and the carbonate system II. Carbon isotopes as a tracer for circulation. The (solid) carbonate connection with. The ocean climate connection

Transcription

1 CO 2 and the carbonate system II Carbon isotopes as a tracer for circulation The (solid) carbonate connection with ocean acidity Climate The ocean climate connection

2 The carbon cycle the carbon cycle involves a lot of chemistry. And a lot of that involves CO 2 and biological transformations

3 The carbon cycle quantified The size of the reservoir is moderated by the fluxes. The deep ocean reservoir is large. It s largely carbonate (DIC)

4 The dissolved inorganic carbonate system in the ocean is a case of buffered acid-base chemistry Absorption of CO 2 by the ocean involves 3 equilibria 1 CO 2(aq) + H 2 0 H 2 CO 3(aq) (carbonic acid) 2 H 2 CO 3(aq) H + (aq) + HCO 3 - (aq)(bicarbonate ion) 3 HCO - 3 (aq) H + (aq) + CO 3-2 (aq) (carbonate ion) 4 Ca ++ (aq) + CO 3-2 (aq) CaCO 3 (calcium carbonate mineral) equation 4 involves the solid phase one and 2 can be combined to: 5 CO 3-2 (aq) + CO 2(aq) + H 2 0 HCO 3 - (aq) + H +

5 Geochemical tracer: carbon isotopes Carbon isotopes 12 C=98.89% 13 C=1.11% 14 C=small and variable

6 Fractionation of carbon is primarily biologically mediated Plants discriminate against 13 C during photosynthesis. The the ultimate 13 C amount varies with plant type and substrate. Libes chapt. 29

7 Fractionation of carbon is primarily biologically mediated Emerson and Hedges (2008) We use it as a tracer for biological processes and for circulation

8 The biological pump moves organic carbon The biological pump moves organic matter with it s depleted isotopic signal from the surface ocean to the deep water masses..

9 The vertical movement of organic carbon can be seen in the isotopes of Carbonate Emerson and Hedges (2008)

10 The conveyor belt circulation And thermohaline circulation moves CO 2 through the system

11 Controls on the fractionation of 13 C Water downwells: DIC enriched Low nutrients High O 2 13 C 12 C 13 C 13 C 12 C 13 C 12 C 12 C 13 C 13 C DIC (in Water) more depleted with increasing age 12 C 12 C 12 C 13 C 12 C 12 C 12 C 12 C C C 12 C 12 C 13 C Porewaters very sensitive to remineralization can be very depleted in 13 C

12 .The deep conveyor belt

13 Atlantic Ocean DIC

14 Pacific Ocean DIC

15 The vertical profile of 13 C reflects the global thermohaline circulation

16 Glacial-interglacial δ 13 C: Atlantic δ 13 C in the Atlantic records changes in deep water carbonate concentrations. Emmerson & Hedges Figure 7.12

17 The deep ocean had more CO Less ventilated more ventilated It looked more like the Pacific today than the Atlantic today Holocene ( ka) Glacial (20-21ka) Southern Ocean 4000

18 The 13 C reflects traces the concentration of CO 2 in the deep ocean Curry and Oppo, 2005 Our tracer is 13 C

19 We can trace changes in deep circulation NADW became NAIW in the LGM Curry and Oppo, 2005 Our tracer is 13 C

20 Carbon and carbonate cycling: The sediment and climate connection The carbon cycle the carbonate portions of the cycle the longer-term reservoir limbs

21 The Dissolved Inorganic Carbonate system in the ocean is a case of buffered acid-base chemistry Absorption of CO 2 by the ocean involves 3 equilibria 1 CO 2(aq) + H 2 0 H 2 CO 3(aq) (carbonic acid) 2 H 2 CO 3(aq) H + (aq) + HCO 3 - (aq)(bicarbonate ion) 3 HCO - 3 (aq) H + (aq) + CO 3-2 (aq) (carbonate ion) 4 Ca ++ (aq) + CO 3-2 (aq) CaCO 3 (calcium carbonate mineral) equation 4 involves the solid phase one and 2 can be combined to: 5 CO 3-2 (aq) + CO 2(aq) + H 2 0 HCO 3 - (aq) + H +

22 The ocean is buffered

23 Carbonate system equilibrium In the dissolved system, the governing equation: CO 3-2 (aq) + CO 2(aq) + H 2 0 HCO 3 - (aq) + H + CaCO 3 CO 3-2 (aq) + CO 2(aq) 2HCO 3 - (aq) + Ca ++ + H 2 0 Calcification (precipitation solid) 2HCO 3 - (aq) + Ca ++ + H 2 0 CaCO 3 + CO 2(aq)

24 Organisms need both carbon dioxide and carbonate Kleypas et al 2005

25 Organisms form calcium carbonate to make their shells O - C O Ca ++ O - CaCO 3

26 The two pumps put CO 2 into the deep ocean

27 The biological pump controls atmospheric CO 2. Biological pump Primary production thermocline Sediments accumulate and dissolve

28 Marine biogeochemical processes affect CO 2 uptake El niño

29 There are different controls on different timescales Ecosystems Climate change

30 The carbon cycle To understand the carbon cycle effect on climate (long term). We have to think past CO 2 and biological transformations and get into the sediments.

31 Carbon and carbonate cycling: The sediment and climate connection The carbonate cycle But first we need to know about sedimentation in general.

32 Sediment distribution on the seafloor

33 Most of the ocean floor is covered by biogenic sediments

34 Most of the ocean floor is covered by carbonate sediments

35 Distribution of carbonate sediments Follows topography WHY?

36 Topography of the seafloor

37 The Atlantic is deep but carbonate rich Why?

38 Depth control of carbonates part 1 What varies with depth? the physical parameters of the water... Varies with depth: Temperature Pressure

39 Saturation curve for CaCO 3 in the ocean This plot describes of CaCO 3 with depth = [Ca++ ][ CO 3-2 ] K sp Terms: Carbonate compensation depth (CCD) Lysocline

40 Depth of the CCD today Follows bathymetry and...

41 Depth control of carbonates part 2 What also varies with depth? Remember previous lecture. How does circulation control CO 2 distributions? What controls dissolution of carbonate? a.k.a. CO 2 distributions? Biopump/age= CO 2 levels

42 Controls on the distribution of CO 2 Water downwells: Low nutrients High O 2 low CO 2 content CO 2 CO 2 CO 2 CO 2 CO 2 CO 2 C org & CaCO 3 C org & CaCO 3 C org & CaCO 3 DIC DIC DIC C org & CaCO 3 DIC DIC DIC DIC content of Water increases with increasing age C org & CaCO 3 DIC C org & CaCO 3 DIC CaCO 3 DIC Corg DIC CaCO 3 DIC DIC C org & CaCO 3 Carbonate Sediments are a source and sink of carbon, both Corg and CO 2

43 Deep circulation and the biological pump. Do it again

44 Depth of the CCD today Follows both bathymetry and CO content

45 Changes in circulation affect the CCD In the glaciation the CCD rose about 1000m More dissolved CO 2 stayed in the ocean and it came out of the atmosphere.

46 Ocean controlled carbon cycling There is a balance between atmosphere and ocean If ocean circulation is changed there is a (moderately) long-term effect on carbon(ate) cycling. Deep water CO 2 affects the sediments But how does that affect the atmosphere? We are talking about CO 2 reservoirs..

47 Controls on the distribution of CO 2 Water downwells: Low nutrients High O 2 low CO 2 content CO 2 CO 2 CO 2 CO 2 CO 2 CO 2 C org & CaCO 3 C org & CaCO 3 C org & CaCO 3 DIC DIC DIC C org & CaCO 3 DIC DIC DIC DIC content of Water increases with increasing age C org & CaCO 3 DIC C org & CaCO 3 DIC CaCO 3 DIC Corg DIC CaCO 3 DIC DIC C org & CaCO 3 Carbonate Sediments are a source and sink of carbon, both Corg and CO 2

48 Record of CO 2 in the atmosphere through time The record of CO 2 levels in the atmosphere measured in bubbles trapped in ice cores

49 Deep circulation and the biological pump. have a lot to answer for