Hot off the press this week is a study on foraminera over the last millennium in the Indo-Pacific Warm Pool – something that you’d think would be relevant to Hansen’s attempts to splice modern instrumental records to core tops ending in the Holocene Optimum. Newton et al 2006 have the following abstract:
Planktonic foraminiferal Mg/Ca and d18O derived sea surface temperature and salinity records from the Makassar Strait, Indonesia, show a long-term cooling and freshening trend, as well as considerable centennial-scale variability during the last millennium. The warmest temperatures and highest salinities occurred during the Medieval Warm Period (MWP), while the coolest temperatures and lowest salinities occurred during the Little Ice Age (LIA). These changes in the western Pacific, along with observations from other high resolution records indicate a regionally coherent southern displacement of the Inter-tropical Convergence Zone during the LIA, with more arid conditions in the northern tropics and wetter conditions in the southern tropics.
The core used for this study, MD9821-60, was collected aboard the Marion Dufrense in 1998 as part of the IMAGES coring program. It was collected at 5 12.07 S, 117 29.20 E from a water depth of 1185 m. This depth is well above the present-day lysocline [Farrell and Prell, 1989], which allows for excellent carbonate preservation. Although the uppermost sediments representing roughly the last 150 years were lost during the coring process, the average Holocene sedimentation rate at this location is well over 100 cm per 1,000 years, making it an ideal core for high resolution studies of hydrographic changes in the Makassar Strait….
The core was sampled continuously at 1 cm intervals, providing a time resolution of less than 10 years
I would have thought that the loss of the sediments for the last 150 years would make it less than ideal for high-resolution studies. It would certainly be nice to see some results for the last 150 years. I’m curious as to how they know that 150 years were lost. In mineral exploration, the core logs are essential parts of the process and lost core is marked on the original core log. There is information on hole MD9821-60 at the IMAGES site, which provides considerable information on the core, but does not say that the top portion of the core was lost (although the length of recovered core is less than the length of the core.)
Their dating model notes an ash layer at 15 cm which is ascribed to the 1815 Tambora eruption. They don’t say why it is dated to the 1815 Tambora eruption as opposed to the 1884 Krakatoa eruption. This might make a difference to the dating. I’d like to ensure that they have not merely assumed that 150 years is missing because of an expectation that modern proxy values would exceed MWP values (which they obviously don’t here.)
Here’s their Figure 1 showing dO18 and Mg/Ca results. They report:
Mean temperature decreased by approximately 1 deg C during the last 1,000 years, while salinity decreased by 0.9. This is consistent with an overall trend of decreasing salinity and temperature in the IPWP throughout the Holocene [Stott et al., 2004].
Taking these results at face value, they evidence a remarkable warming of the Warm Pool by almost 2 deg C in less than a decade at the turn of the 19th Century. It would be interesting to see if there are contemporary historical evidence of this remarkable event.
They attribute changes in the Warm Pool to changes in the north-southing of the ITCZ – something which I proposed as an explanation for Kim Cobb’s coral values as an alternative to a cold MWP Pacific – which is obviously nowhere in evidence here.
Newton, A., R. Thunell, and L. Stott (2006), Climate and hydrographic variability in the Indo-Pacific Warm Pool during the last millennium, Geophys. Res. Lett., 33, L19710, doi:10.1029/2006GL027234.