DOI: 10.25921/bkrj-5535
title: NOAA/WDS Paleoclimatology - Simulations of glacial climate and ocean biogeochemistry with the CSIRO Mk3L v1.0

description: The ocean's ability to store large quantities of carbon, combined with the millennial longevity over which this reservoir is overturned, has implicated the ocean as a key driver of glacial–interglacial climates. However, the combination of processes that cause an accumulation of carbon within the ocean during glacial periods is still under debate. Here we present simulations of the Last Glacial Maximum (LGM) using the CSIRO Mk3L-COAL (Carbon–Ocean–Atmosphere–Land) earth system model to test the contribution of physical and biogeochemical processes to ocean carbon storage. For the LGM simulation, we find a significant global cooling of the surface ocean (3.2 °C) and the expansion of both minimum and maximum sea ice cover broadly consistent with proxy reconstructions. The glacial ocean stores an additional 267 Pg C in the deep ocean relative to the pre-industrial (PI) simulation due to stronger Antarctic Bottom Water formation. However, 889 Pg C is lost from the upper ocean via equilibration with a lower atmospheric CO2 concentration and a global decrease in export production, causing a net loss of carbon relative to the PI ocean. The LGM deep ocean also experiences an oxygenation ( &gt; 100 mmol O2 m-3) and deepening of the calcite saturation horizon (exceeds the ocean bottom) at odds with proxy reconstructions. With modifications to key biogeochemical processes, which include an increased export of organic matter due to a simulated release from iron limitation, a deepening of remineralisation and decreased inorganic carbon export driven by cooler temperatures, we find that the carbon content of the glacial ocean can be sufficiently increased (317 Pg C) to explain the reduction in atmospheric and terrestrial carbon at the LGM (194 ± 2 and 330 ± 400 Pg C, respectively). Assuming an LGM–PI difference of 95 ppm pCO2, we find that 55 ppm can be attributed to the biological pump, 28 ppm to circulation changes and the remaining 12 ppm to solubility. The biogeochemical modifications also improve model–proxy agreement in export production, carbonate chemistry and dissolved oxygen fields. Thus, we find strong evidence that variations in the oceanic biological pump exert a primary control on the climate.
description: Simulations of glacial climate and ocean biogeochemistry with the CSIRO Mk3L.

This dataset includes both the physical and biogeochemical output of simulations performed with the CSIRO Mk3L v1.2 Earth System Model under broadly Pre-Industrial (PI; 1950 CE) and Last Glacial Maximum (LGM; 21,000 BCE) climates.
Two simulations using the fully coupled Earth System Model, with atmosphere, ocean and sea-ice components, were undertaken by forcing the model with the boundary conditions of each climate state. The boundary conditions included appropriate greenhouse forcing using CO2 equivalents and orbital parameters.
Climatologies of sea surface temperature, sea surface salinity, and x and y vectors of sea surface wind stresses were produced by both the PI and LGM coupled experiments and were used to force the ocean general circulation model. Additional climatologies of sea ice fractional cover, sea surface wind speeds, and net incident short-wave radiation were important for forcing the biogeochemical model. These climatologies are available.
Also available are the three-dimensional global annual averages of oceanic properties for both PI and LGM climates. These include temperature, salinity, oxygen, apparent oxygen utilisation, dissolved inorganic carbon, alkalinity, calcite saturation state, aragonite saturation state, phosphate and iron concentrations.
A full description of the CSIRO Mk3L v1.2 can be found in both:
Phipps, S. J., Rotstayn, L. D., Gordon, H. B., Roberts, J. L., Hirst, A. C., and Budd, W. F.: The CSIRO Mk3L climate system model version 1.0 - Part 1: Description and evaluation, Geosci. Model Dev., 4, 483-509, doi:10.5194/gmd-4-483-2011, 2011.
Phipps, S. J., Rotstayn, L. D., Gordon, H. B., Roberts, J. L., Hirst, A. C., and Budd, W. F.: The CSIRO Mk3L climate system model version 1.0 - Part 2: Response to external forcings, Geosci. Model Dev., 5, 649-682, doi:10.5194/gmd-5-649-2012, 2012.
A complete description of the biogeochemical ocean model that was used (Mk3L-COAL) can be found in Appendix A of:
Matear, R. J. and Lenton, A.: Quantifying the impact of ocean acidification on our future climate, Biogeosciences, 11, 3965-3983, doi:10.5194/bg-11-3965-2014, 

Contact: pearse.buchanan@utas.edu.au for any question on the dataset content and provenance
         paola.petrelli@utas.edu.au for questions or issues with file accessibility

Guide to the data files:

  |Pre-Industrial output|
O-PI_GCM.nc         = Physical fields for the Pre-Industrial climate
PIice.nc           = Sea ice concentration fields for the Pre-Industrial climate
O-PI.nc             = Biogeochemical fields for the Pre-Industrial climate
O-PI_LGM-co2.nc     = Biogeochemical fields for the Pre-Industrial climate (with atmospheric CO2 set at 185 ppm)
O-PI_LGM-sol.nc     = Biogeochemical fields for the Pre-Industrial climate (with atmospheric CO2 set at 185 ppm, and surface conditions of the Last Glacial Maximum)
O-PI_LGM-ice.nc     = Biogeochemical fields for the Pre-Industrial climate (with atmospheric CO2 set at 185 ppm, and sea ice of the Last Glacial Maximum) 

  |Last Glacial Maximum output|
O-LGM_GCM.nc        = Physical fields for the Last Glacial Maximum climate
LGMice.nc           = Sea ice concentration fields for the Last Glacial Maximum climate
O-LGM.nc            = Biogeochemical fields for the Last Glacial Maximum climate
O-LGM_BGC-poc.nc    = Biogeochemical fields for the Last Glacial Maximum climate (with 10x potential export production)
O-LGM_BGC-rem.nc    = Biogeochemical fields for the Last Glacial Maximum climate (with increased export of organic matter to depth)
O-LGM_BGC-pic.nc    = Biogeochemical fields for the Last Glacial Maximum climate (with no production of calcifying organisms)
O-LGM_BGC-all.nc    = Biogeochemical fields for the Last Glacial Maximum climate (with all above biogeochemical modifications)

  |Observational datasets used for validation|
Levitus_obs.nc              = Observations of modern fields from Levitus, Levitus (2001) World Ocean Database, Vol 13, US Department of Commerce, National Ocean and Atmosphere Agency. 

  FIELDS FROM THE GENERAL CIRCULATION MODEL:    
    CDEPTHM - Maximum depth of convection                                   -   metres (m)
    MOEA    - Eddy-induced meridional overturning in the Atlantic Ocean     -   sverdrups (1e6 m3/s)
    MOEG    - Eddy-induced meridional overturning in the Global Ocean       -   sverdrups (1e6 m3/s)
    MOEI    - Eddy-induced meridional overturning in the Indian Ocean       -   sverdrups (1e6 m3/s)
    MOEP    - Eddy-induced meridional overturning in the Pacific Ocean      -   sverdrups (1e6 m3/s)
    MOLA    - Large-scale meridional overturning in the Atlantic Ocean      -   sverdrups (1e6 m3/s)
    MOLG    - Large-scale meridional overturning in the Global Ocean        -   sverdrups (1e6 m3/s)
    MOLI    - Large-scale meridional overturning in the Indian Ocean        -   sverdrups (1e6 m3/s)
    MOLP    - Large-scale meridional overturning in the Pacific Ocean       -   sverdrups (1e6 m3/s)
    MOTA    - Total meridional overturning in the Atlantic Ocean            -   sverdrups (1e6 m3/s)
    MOTG    - Total meridional overturning in the Global Ocean              -   sverdrups (1e6 m3/s)
    MOTI    - Total meridional overturning in the Indian Ocean              -   sverdrups (1e6 m3/s)
    MOTP    - Total meridional overturning in the Pacific Ocean             -   sverdrups (1e6 m3/s)
    RES     - Barotropic streamfunction                                     -   sverdrups (1e6 m3/s)
    SMFMER  - Meridional wind stress                                        -   pascals (N/m2) 
    SMFZON  - Zonal wind stress                                             -   pascals (N/m2)
    STFHT   - Surface heat flux                                             -   Watts per m2 (W/m2)
    STFSAL  - Surface salinity tendency                                     -   psu per second (s-1)
    U       - Zonal velocity                                                -   metres per second (m/s)
    V       - Meridional velocity                                           -   metres per second (m/s)
    W       - Vertical velocity                                             -   metres per second (m/s)

  FIELDS FROM THE SEA ICE MODEL:
    ICEMAX  - Maximum annual sea ice extent                                 -   fractional cover per metre squared (m-2)
    ICEMIN  - Minimum annual sea ice extent                                 -   fractional cover per metre squared (m-2)
    ICEAVE  - Annual average sea ice extent                                 -   fractional cover per metre squared (m-2)

  FIELDS FROM THE BIOGEOCHMEICAL MODEL:
    PCO2    - Partial pressure of carbon dioxide at surface                 -   Parts per million (ppm)
    POC     - Particulate Organic Matter production at surface              -   grams carbon per metre squared per year (g C m-2 yr-1)
    PIC     - Particulate Inorganic Matter production at surface            -   grams carbon per metre squared per year (g C m-2 yr-1)
    WIND2   - Sea surface wind speed squared                                -   metres per second (m/s)   
    TEMP    - Potential temperature                                         -   Celcius
    SAL     - Salinity                                                      -   PSU
    OXY     - Oxygen concentration                                          -   millimoles per cubic metre (mmol/m3)
    DIC     - Dissolved Inorganic Carbon concentration                      -   millimoles per cubic metre (mmol/m3)
    ALK     - Alkalinity concentration                                      -   millimolar equivalents per cubic metre (mmol Eq. / m3)
    PO4     - Phosphate concentration                                       -   millimoles per cubic metre (mmol/m3)
    FE      - Bioavailable iron concentration                               -   micromoles per cubic metre (umol/m3)
    OMEGAAR - Aragonite saturation state                                    -   Omega
    OMEGACA - Calcite saturation state                                      -   Omega
    
Provided Keywords: Nitrogen cycle, carbon cycle, Marine ecosystem, Phytoplankton, Carbon dioxide, climate change