Sensitivity of ocean carbon tracer distributions to particulate organic flux parameterizations

Abstract

Vertical carbon fluxes of particulate organic carbon (POC) from the euphotic zone to the deep sea are of significant importance for the carbon cycle in the oceans. In this study, fluxes of POC below the euphotic zone in the ocean were simulated with the Hamburg ocean carbon cycle model (HAMOCC5.1) by using different POC-flux parameterizations and compared with sediment trap data. The simulated POC fluxes in dependence of regional environmental changes are in reasonable agreement with sediment trap data below 1000 m in the oceans, if a regionally variable POC flux parameterization is considered. Specifically, model-data differences in the Southern Ocean are sensitive to the vertical mixing and to regional variations of the ballasting minerals of the POC flux. Overall, selection of different POC flux parameterizations considerably changes the geochemical distributions in the deep sea.

Table 1. Experiment names and descriptions.

Table 2. Modeled export production (g C m-2 yr-1), net primary production (NPP, g C /m^2 yr),
and f-ratio from experiment BAL compared with observational estimates compiled by Lutz et al.
[2002].

Figure 1. Locations of sediment trap data [after Klaas and Archer, 2002].

Figure 2. Simulated export production in g C m-2 yr-1from the surface layer in the HAMOCC5.1. The contour interval in each plot is 10 g C/m^2 yr. All plots are from a 10,000 year model integration. a) Experiment REF, b) Experiment REFD, c) MARTIN, and d) BAL.

Figure 3. POC Fluxes in g C m-2 yr-1, models compared with sediment trap data (purple points)
for experiments BAL (blue diamonds), REF (green squares), REFD (orange triangles), and
MARTIN (red squares). Error bars are standard 30% error on sediment trap measurements. a)
North Atlantic, 34ºN, 21ºW, data at 1160 m, 1980 m, and 4480 m from a Parflux 7 trap collected
in 1989 and 1990 [Honjo and Manganini, 1993]. b) Subtropical S. Atlantic, 29ºS, 15ºE, data at
2516 m depth from collected in 1992-93 [Fischer et al., 2000]. c) W. Subtrop. N. Atlantic,
14ºN, 54ºW, data at 988 m , 3755 m, and 5068 m from a Parflux 2 trap collected in 1977-1978
[Honjo, 1980]. d) Arabian Sea, 15ºN, 65ºE, data at 2907 m, 2913 m, and 3021 m from a Parflux
6 trap collected in 1986-88 [Haake et al., 1993]. e) Equatorial Pacific, 0ºN, 140ºE, data at 1130
m and 3130 m from a Parflux 6 trap collected in 1988-89 [Kempe and Knaack, 1996]. f)
Southern Ocean, 57ºS, 170ºW, data at 1031 m from a Parflux 6 trap collected in 1996-97 [Honjo
et al., 2000].

Figure 4. Preindustrial distribution of DIC in µmol kg-1 at 3,000m depth. a) Data from
GLODAP (Global Ocean Data Analysis Project) [Key et al., 2002], b) experiment REF minus
GLODAP data, c) experiment REFD minus GLODAP data, d) experiment BAL minus
GLODAP data, e) experiment MARTIN minus GLODAP data. (Note: For total error of
GLODAP data, see auxillary figures).

Figure 5. Left column: model PO4 distribution in µmol kg-1 at 3000 m depth normalized to
WOA 2001 data with factor of 1.1925 to adjust for mass lost by sediments for experiments a)
REF, b) REFD, c) MARTIN, d) BAL, and e) PO4 from WOA 2001 [Conkright et al., 2002]. Gray
areas in the figure are areas with no data. Right column: PO4* distribution in µmol kg-1 at 3000
m depth for experiments i) REF, j) REFD, k) MARTIN, l) BAL, and m) PO4* calculated using
WOA 2001 PO4 and O2 data. See text for definition of PO4* (eq. 6).

Figure 6. Alk* distribution in µmol kg-1 at 3000 m depth for experiments a) REF, b) BAL, c)
MARTIN, and d) BAL. e) Alk* calculated using GLODAP alkalinity data and WOA 2001
salinity data. See text for definition of Alk* (eq. 7).

Figure 7. Total DIC difference plots. a) Experiment BALEF1 minus Experiment BAL, Pacific
section, 160º W. b) Experiment BALEF2 minus BAL, Pacific section.

Figure 8. Alkalinity difference plots. a) Experiment BALPP1 minus Experiment BAL, Pacific
section, 160º W. b) Experiment BALPP2 minus Experiment BAL, Pacific section.