The Levitus estimate for the closest 1×1 gridcell is much lower than the alkenone estimates as shown in the graph below. ❋ Unknown (2007)
The alkenone-derived SST records show diverging linear trends over the last 7000 years Figures 3 and 4a. ❋ Unknown (2007)
It appears to me that the interest is not so much quantitative at this point but qualitative in that they want to direct attention to a point that the seasonal variations might be of such a magnitude that alkenone proxy indications of a warmer Holocene than present might be reversed with more precise and seasonal resolved data. ❋ Unknown (2007)
Examples of alkenone-derived SST records (circles) and their linear trends (solid lines) evaluated from 20 cores, whose positions are shown on the map Kim and Schneider, 2004; see also Kim et al., 2004, Table 1. ❋ Unknown (2007)
The SST reconstructions were stated in the article to be limited to alkenone proxies because of the need for “consistency”. ❋ Unknown (2007)
This figure also shows the very low resolution of most of the alkenone records discussed in this article. ❋ Unknown (2007)
The alkenone proxies are to be relegated to a measure of seasonal temperature that, while being higher than today, is averaged out by lower temperatures in seasons as computer runs indicate when the alkenone proxy was temperature insensitive or dormant if you will. ❋ Unknown (2007)
The use of this simple criterion would seem to me to make the study suspect for cherry picking if non-alkenone proxies that went against the trends were not included in the study or at least mentioned. ❋ Unknown (2007)
They go on to attempt to show that computer model climate simulations can provide seasonal change resolution for the Holocene Optimum period to present that the alkenone results cannot. ❋ Unknown (2007)
This lack of representation from an obviously essential region is presumably because of the restriction of their proxies to alkenone SST, which eliminates Stott et al 2004 from consideration it used Mg/Ca and dO18. ❋ Unknown (2007)
If the alkenone production is thought to be highest during the month with the warmest water temperature in the mixed layer, then the resemblance of reconstructed trends with the simulated trends of local summer can be taken as an indication that the time of maximum production may have changed with the insolation signal. ❋ Unknown (2007)
Lorenz et al. 2006 give a less than confident observation of phytoplankton growth and the resulting relationship of the alkenone proxy relationship to seasonal temperatures: ❋ Unknown (2007)
Orbitally driven insolation forcing on Holocene climate trends: Evidence from alkenone data and climate modeling. ❋ Unknown (2007)
Since the tropics and extra tropics have nearly equal areas we can say that from the alkenone data alone that 7000 years BP was globally about 0.61 degrees C warmer than present. ❋ Unknown (2007)
I guess that since the Lorenz paper stated it wanted to use only alkenone proxies to be “consistent” that it meant that they did not want to even mention other proxy papers. ❋ Unknown (2007)
Their proxy is alkenone SST estimates collated in the following location: a site which unfortunately is password protected. ❋ Unknown (2007)
That is why I am interested in seeing other proxy data from this period that is not as seasonal as the alkenone proxy is claimed to be and something that might test the computer simulations results for seasonal variations. ❋ Unknown (2007)
From the alkenone proxy data in Lorenz (2006), I calculated average tropic and extratropic temperature changes to present and came up with: tropics (30N to 30S) change from 7000 years BP (the Holocene Optimum) to present = 0.23 degrees C and for the extratropics (all other areas of the globe) this change = -1.45 degrees C. ❋ Unknown (2007)
Global core top sediment calibrations of the alkenone paleothermometer Miller et al., 1998 are most consistent with mean annual SSTs at 0-M water depth. ❋ Unknown (2007)
