One of the two strongest contributors to higher temperatures in Moberg’s 20th century proxies is higher incidence of subpolar glob. bulloides foraminifera in the Arabian Sea off Oman, actually a direct indicator of cooler SST.
The Arabian Sea series of Moberg et al [2005] (see their Supplementary Figure 1, series #11) is one of the few Moberg low-frequency sites where the 20th century values significantly exceed MWP values. This record is described in their Supplementary Information as follows:
A combination of two marine sediment records from the Arabian Sea in which the percentage of the foraminifera Globigerina bulloides reflects the extent of ocean up-welling, which is determined by the strength of monsoons, which in turn indirectly reflect both summer and winter large-scale temperature changes through the differential seasonal heating and cooling of the Asian continent and surrounding oceans… Although this record reflects temperatures only indirectly, it was included to improve the balance in the geographical distribution of proxy sites.
It is one of two records which is not calibrated to temperature. Gupta et al. [2003] describe the occurrence of the glob. bulloides diatom as follows:
Cooling of the sea surface associated with coastal and open ocean upwelling promotes the blooming of distinct fauna and flora. The biological response to the monsoonal activity in the surface water column is preserved as increased abundance of the planktic foraminifer Globigerina bulloides…Advantages of this proxy are (1) its unique association with the summer monsoon (G. bulloides has a subpolar habitat and would be absent in the tropics except for wind-driven upwelling), (2) linear correlation with the surface cooling due to upwelling, apparently unbiased by other influences,
Gupta et al. go on to argue that increased monsoon activity is associated with changes in the North Atlantic — cold periods lead to weak monsoons, warm periods to active monsoons. Under this theory, the increased incidence of glob. bulloides in the 20th century offshore Oman is indirect evidence of a warmed North Atlantic. But it is direct evidence of cooler SST offshore Oman. If the objective of including this record is to “improve the geographical balance”, wouldn’t it make more sense to change the sign (as Moberg did with some tree ring series)? I find it a little strange that one of the two strongest contributors to Moberg’s low-frequency warming in the 20th century is an increased incidence of subpolar foraminifera in the tropics.
REFERENCES:
Anderson, D. M., Overpeck, J. T. & Gupta, A. K. Increase in the Asian SW Monsoon During the Past Four Centuries. Science 297, 596-599 (2002).
Gupta, A. K., Anderson, D. M. & Overpeck, J. T. Abrupt changes in the Asian southwest monsoon during the Holocene and their links to the North Atlantic Ocean. Nature 421, 354-357 (2003).
Overpeck, J., Anderson, D., Trumbore, S. & Prell, W. The southwest Indian Monsoon over the last 18 000 years. Clim. Dyn. 12, 213-225 (1996).
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3 Comments
So it indicates warm weather in the area in general but also cold temp at the sea surface? What are they interested in? total surface temp? ARe ocean surfaces included?
Ocean surface temperatures SST are the major component of the HadCRU temperature index. You wold think that an index of cold SST would first and foremost be construed as evidence of cold SST. The theory seems to be that there is a “tele-connection” betweeen cold SST offshore Oman and a warm NH average. However, their justification for this proxy was not the need for a tele-connected indicator for NH temperatures but the absence of a local proxy. I’m not saying that any of this makes sense: I think that it’s ridiculous.
Also the proxy is hugely non-normal.
a. What do you mean by non-normal?
b. How do they bring this data into the grid cell computation? If you accept the tele-argument then there might be a much larger area that is hot when this small area is cold, no?
c. How does one deal with this small cold area? Sure the actual surface is colder, but the overall ocean (in depth) is warmer, no? (I’m “stirring” it). What matters? Could one compensate for CO2 warmth by stirrring the ocean? How much of a heat sink is there? Do you run out? sorry my questions so diffuse.
d. If I get your last point, they justify this series by the lack of a proxy near Oman but what it indicates is temp in India? Even if it is a valid proxy (via tele argument) one should consider it a proxy of that remote area, not the place where the data was gathered. For instance, if I sample radioactive nuclides for evidence of aboveground testing in the ice of the western Rockies, I’m not accounting for testing in Colorado. I’m accounting for testing in Neveda. And the tele argument might be quite legit. (Same thing with acid rain in New England reflecting distant factory releases of sulfates)
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