1 Oceans from Space, a Once-a-Decade Review of Progress
5
1.4 Ocean Colour and a Change in Global Productivity
As oceanographers, we need to ask what the ocean has contributed to this change.
Has global ocean productivity (or biomass, as we effectively measure it) increased?
If the total increase of ocean productivity is as large as that on land, then presumably
the Keeling curve would not show an increase in its annual cycle amplitude, as the
northern summer decrease would be offset by an increase in total productivity of the
southern ocean.
The time series we have for this is poor, to say the least. It has been suggested
that the average biomass deduced from the entire CZCS mission (1978–1986) was
less than that more recently deduced by SeaWiFS for 1997–2004 (Antoine et al.,
2005). Changes within the SeaWiFS data time series have also been reported (Gregg
et al., 2005; Behrenfeld et al., 2006), and shown to be strongly affected by the ElNino/La-Nina in 1997–1999. If these data are plotted as time series (Fig. 1.4), they
lack the impressive impact of a multi-point plot, but they can be important nonetheless. The patterns of change seem related to an increase in area of oligotrophic
waters in ocean basin gyres (Polovina, 2008).
In determining any trend in biomass, we come up against the continuing problem of providing long-term, stable, “climate quality” time series of global ocean
optical data. Ocean color has already experienced the 10-year gap between CZCS
and SeaWiFS. In an open letter to the ocean optics community Siegel et al. (2008)
stated “It appears likely that the ocean biology and biogeochemistry communities
will (again) face a multi-year gap in our climate data records.” A problem which I
would summarize in verse as:
We’ve needed one more SeaWiFS for many, many years
Instead we’ve bought 2 MODISs, a MERIS and a VIIRS
I should stress that both MODIS and MERIS have brought their own scientific
and operational successes, but they were not designed as simple, stable instruments.
0.8
0.9
1
1.1
1.2
1.3
1970
1980
1990
2000
2010
2020
Year
Relative global ocean biomass
SeaWiFS
CZCS
Fig. 1.4 Relative change in global ocean biomass from CZCS and SeaWiFS. Filled diamonds:
Antoine et al. (2005). Open squares: Gregg et al. (2005). Open triangles: Behrenfeld et al. (2006)
5
1.4 Ocean Colour and a Change in Global Productivity
As oceanographers, we need to ask what the ocean has contributed to this change.
Has global ocean productivity (or biomass, as we effectively measure it) increased?
If the total increase of ocean productivity is as large as that on land, then presumably
the Keeling curve would not show an increase in its annual cycle amplitude, as the
northern summer decrease would be offset by an increase in total productivity of the
southern ocean.
The time series we have for this is poor, to say the least. It has been suggested
that the average biomass deduced from the entire CZCS mission (1978–1986) was
less than that more recently deduced by SeaWiFS for 1997–2004 (Antoine et al.,
2005). Changes within the SeaWiFS data time series have also been reported (Gregg
et al., 2005; Behrenfeld et al., 2006), and shown to be strongly affected by the ElNino/La-Nina in 1997–1999. If these data are plotted as time series (Fig. 1.4), they
lack the impressive impact of a multi-point plot, but they can be important nonetheless. The patterns of change seem related to an increase in area of oligotrophic
waters in ocean basin gyres (Polovina, 2008).
In determining any trend in biomass, we come up against the continuing problem of providing long-term, stable, “climate quality” time series of global ocean
optical data. Ocean color has already experienced the 10-year gap between CZCS
and SeaWiFS. In an open letter to the ocean optics community Siegel et al. (2008)
stated “It appears likely that the ocean biology and biogeochemistry communities
will (again) face a multi-year gap in our climate data records.” A problem which I
would summarize in verse as:
We’ve needed one more SeaWiFS for many, many years
Instead we’ve bought 2 MODISs, a MERIS and a VIIRS
I should stress that both MODIS and MERIS have brought their own scientific
and operational successes, but they were not designed as simple, stable instruments.
0.8
0.9
1
1.1
1.2
1.3
1970
1980
1990
2000
2010
2020
Year
Relative global ocean biomass
SeaWiFS
CZCS
Fig. 1.4 Relative change in global ocean biomass from CZCS and SeaWiFS. Filled diamonds:
Antoine et al. (2005). Open squares: Gregg et al. (2005). Open triangles: Behrenfeld et al. (2006)