1. Recap on
biological
oceanography

2. CO2
changes in the last 50 yr
Oceans
Biosphere
Rock Weathering 2

3. Carbon Cycle

4. The Carbonate System sources of inorganic carbon
from dissolved CO2 gas
from dissolution of Calcium Carbonate
Total dissolved inorganic carbon

5. Carbon Dioxide and Carbonate system
Carbonic Acid
Bicarbonate Ion
Carbonate

6. O2
CO2 pH
(m)
acid
basic

7. Dissolved Gases in the Ocean
Oxygen profile
compensation depth
Respiration:
Animal, plants and microbial decomposition
low oxygen environment

8. Distribution of Carbon species in water+ -

10. from GLODAP climatology

11. Higher CO2 levels will generally be detrimental to calcifying organisms and that food web structures and biodiversity will likely change,
Coccolithophores
Forams
Corals
calcite
calcite
aragonite
but it is not clear how this might impact overall productivity and top level predators (e.g. fish).

12. Biogeochemical Controls and Feedbacks on the Ocean Primary Production
3) Subpolar Gyres
2) Upwelling Regions
1) Subtropical Gyres
Photosyntesis is the main contributor to the development of oxygen in the billion years ago organic C deposits.
4) HNLC regions
What can explain the chlorophyll distribution?

13. What are the controls on Export Production?
Ocean nutrient inventory
Nitrogen appears to be the control during modern time.
Where nitrogen can be brought at the surface
there is higher productivity: Upwelling regions
and subpolar gyres
Exception: HNLC regions, particularly in the
Southern ocean The Iron Problem

14. Map of annual average nitrate concentrations in
Southern Ocean HNLC
Map of annual average nitrate concentrations in
the surface waters of the oceans. Data from
Levitus, World Ocean Atlas, 1994.

15. Advanced Very High Resolution Radiometer
(AVHRR) images of particle transport in the
atmosphere between June and August. 

16. Biophysical interactions
Wind-driven gyre circulation for surface distributions;
MOC for concentrations at depth

17. North-south sections of (a) temperature, (b) salinity, and (c) oxygen along the 30oW
transect in the Atlantic ocean. Note the salinity tongues indicating the interleaving of
water masses from sources in the Antarctic and the North Atlantic.

18. Pacific

19. Summaring
The large scale wind-driven circulation explains the (large scale) distribution of chlorophyll.
We need to consider the biology to explain the distribution of nitrate (remember the high latitudes and the iron problem!)
The thermohaline circulation
explains the vertical distributions
of oxygen and NO3 and the
differences between the basins at depth

20. The Nitrogen Cycle The Demand Side. The Supply Side Denitrification.
Alternative pathways to N2.
The Supply Side
Nitrogen Fixation: the usual suspects.
“New” diazotrophs and how they work.

21. Who Cares? Broad reaches of the ocean are N-limited.
Recycling of N within the water column supports biological production, but…
Injection of new N into the upper water column is required to support export production.
The N and C cycles are tightly coupled through biological production of organic matter (C:N ≈ 7).
The N cycle therefore plays a key role in regulating the C cycle!

22. Oceanic N Cycle Schematic
Fixation N2
Nitrification
Mineralization
NH4
NO3
Uptake
Phytoplankton
Grazing
Mix Layer
depth
Chlorophyll
Zooplankton
Mortality
Large
detritus
Water column
Susp.
particles
Nitrification N2
NH4
NO3
Denitrification
Aerobic mineralization
Organic matter
Sediment

23. Major Biological Transformations of Nitrogen
(Inspired by Codispoti 2001and Liu 1979)

25. The major oceanic inputs and outputs of combined N are largely separated in space.
Denitrification is restricted to sediments and anoxic water masses.
N2-fixation is common in oligotrophic surface waters (e.g., the central gyres of the major ocean basins).

26. N* = 0.87( [NO3-] - 16[PO43-] + 2.9) (Gruber & Sarmiento 1997)
N* Distribution Shows Interplay Between N2-Fixation and Denitrification
N* = 0.87( [NO3-] - 16[PO43-] + 2.9) (Gruber & Sarmiento 1997)

27. What else?
Time-dependence: waves, eddies, convection, ocean-atmosphere interactions
and various modes of variability from intraseasonal to inderdecadal
(ENSO, NAO, PDO, NPGO ….)

28. La Nina
conditions
El Nino
conditions

29. in the North Pacific
Pacific Decadal Oscillation

30. Mean Sea Level Pressure
Anomaly PDO Negative Phase
Anomaly PDO Positive Phase

31. + - +

33. The NPGO (North Pacific Gyre Oscillations)
Di Lorenzo
et al.
GRL 2008
North Pacific dominant mode of oceanic variability: the PDO and NPGO (left), are driven by the first two dominant modes of atmospheric variability evident in sea level pressure, the Aleutian Low variability and the NPO.

35. Variability of subsurface nitrate (NO3)
Variability of subsurface nitrate (NO3). (A) Mean subsurface (150m) NO3 from ROMS model over (B) First mode of variability for model subsurface (150m) NO3 anomaly inferred from EOF1. (C) Timeseries of NPGO index (black) compared to PC1 of NO3 (R=0.65, 99%), observed mix layer NO3 at Line-P [Peña and Varela, 2007], and observed NO3 from CalCOFI program (R=0.51, 95%).

36. The North Atlantic Oscillation Index
The NAO index shows large variations from year to year. This interannual signal was especially strong during the end of the 19th century.
Sometimes the NAO index stays in one
phase for several years in a row. This
decadal variability was quite strong in
the second half of the 20th century. 36

37. SST Anomalies [C] Positive NAO Negative NAO Wet Dry Dry Wet
Stronger Currents
more storms
Dry
Dry
fewer storms
Wet
Weaker Currents
Negative NAO 37

38. Impacts of the NAO
Martin Visbeck 38