The mystery interval, the last glacial transition

ABSTRACT
The last deglaciation in the Northern Hemisphere was interrupted by two major stadials, the so-called “Mystery Interval” (17.5–14.5 ka) and the Younger Dryas (12.9–11.7 ka). During these events, the North Atlantic region was marked by cold surface conditions, yet simultaneous glacier and snowline retreat. Rerouting of Laurentide Ice Sheet meltwater from the Gulf of Mexico to an eastern or northern spillway may have reduced meridional overturning circulation at the onset of the Younger Dryas. However, this hypothesis has not been tested for the Mystery Interval. Paired Mg/Ca and 18O measurements on foraminifera
from laminated Orca Basin sediments in the Gulf of Mexico, constrained by 35 14C dates, document the timing of meltwater input with subcentennial resolution. Isolating the 18O of seawater (termed 18OGOM) reveals three major melting episodes from ca. 17.5 ka until
12.9 ka, followed by a rapid cessation, consistent with meltwater rerouting at the onset of the Younger Dryas. Conversely, inferred meltwater flow to the Gulf of Mexico during the Mystery Interval does not support a simple routing event, but is consistent with glacier and snowline retreat. We suggest that summer melting of Northern Hemisphere ice sheets during this stadial may have been an important mechanism for enhanced winter sea-ice formation, hypercold winter conditions, and enhanced seasonality in the North Atlantic region.

Denton et al 2006 investigate the time period between the beginning of Heinrich event #1 (H-1) and the onset of the Bølling/Allerød warm interstadial and find apparently mutually contradictory records. Whereas several isotope signatures indicated cold conditions, temperate mountain glaciers were nevertheless receding at a high rate. Therefore, they term this period the “Mystery Interval”.

They identify hyper cold winters, yet, massive retreat of glaciers on the Northern hemisphere. They propose that H1 effectively shut down the Thermohaline Current which caused massive sea ice expansion while the retreat of temperate mountain glaciers reflects warming summer conditions brought on by rising atmospheric CO2. I will demonstrate with a few examples from a plethora of available research, that the to be predicted logical tests from this hypothesis fail

If extensive winter sea ice is dominating the Arctic sea, then it certainly has it’s impact on the Arctic continent, eg Siberia. Hence we must find the same hyper-cold conditions back in the period 17,500-14,500 Cal BP

Hubberten et al 2004 summarizes the result of studies of the Late Weichselian periglacial environment of Northern Eurasia and find from multiple proxies a remarkable warming around 15Ka BP (18,7 Ka Cal BP), for instance using insect assemblages in the area of the Laptev sea (fig6 pp1339, see below), they define the “warmest tundra steppe” between about 10Ka BP and 15 Ka BP (11,2-18,7 Ka Cal BP)with an dramatic increase of xerophilous insects from an average <20% to a 60-70% spike around 14 Ka BP (15.7 Ka Cal BP). It may be noted that the NH summer isolation at that time was halfway the transition from a minimum around 22-23 Ka to a maximum around 9-10 Ka, which would not suffice to explain the ususual high temperatures. It may be clear that extensive sea ice in the Laptev sea would not compare to these results.

Extensive sea ice is furthermore not compatible with the results of Lagerklint & Wright (1999) using high-resolution faunal, isotopic, and sedimentologic data from North Atlantic core V29-191 to show that sea-surface temperatures increased from 17.5 to 17.3 ka but also contend that during HE1 the sea surface temperature decreased again.

Denton et al suggested that the Mediteranian sea was also unusual cold however Carboni et al (2005) investigate the ratio of plancktonic cold and warm taxa in the Tyrrhenian Sea, and find warming already at 16,3 Ka 14C BP and progressing climate fluctuations as of 15.0 Ka 14C BP at zone B (para 4.3.1 and 4.3.e) which converts to 19.0 and 17.7 Ka cal BP using the Marine04 calibration table of Reimer et al 2004. Note that although Carboni et al mention calibrated dates in table1, they do not use them in the text)

Hill et al 2006 find also indication early deglacial warmth 2 ka before the formal termination and remark that those findings "are consistent with a growing number of records from around the globe that exhibit pre-Bølling warming prior to Termination IA, and extends the record of such processes to the northern Pacific


Discussion
The records do not support the hypothesis of Denton et al, which attempt to explain the contradictions in the records of the mystery interval. In such an unusual situation, where all logic seems to crumble, it may seem feasible to re-evaluate the logic instead. Paleo-temperature is inferred from proxies like variation in species with known temperature responses, glacial behavior and isotope ratios. When both the glaciers and the biota proxies suggest warming, and also the southern hemisphere did so and only the ice-water isotope proxies deny that, it seems feasible to re-investigate the robustness of the latter. Since many records also suggest a strong aridity during the mystery interval it may be feasible to test the precipitation isotope records against sensitivity to aridity.

References

Carboni G, L Bergamin, L Di Bella, B Landini, L Manfra, P Vesic 2005, Late Quaternary
paleoclimatic and paleoenviromental changes in the Tyrrhenian Sea, Quaternary Science
Reviews Volume 24, Issues 18-19 , October 2005, pp 2069-2082

Denton, G.H, WS Broecker, RB Alley,2006; The mystery interval 17.5 to 14.5 kyrs ago, Pages Volume 14 No 2 August 2006, pp14-17

Hill T.M., J.P. Kennett, D.K. Pak, R.J. Behl, C. Robert and L. Beaufort 2006 Pre-Bølling warming in Santa Barbara Basin, California: surface and intermediate water records of early deglacial warmth, Quaternary Science Reviews Volume 25, Issues 21-22, November 2006, Pages 2835-2845

Hubberten et (21) al 2004 The periglacial climate and environment in northern Eurasia during the Last Glaciation, Quaternary Science Reviews 23 (2004) 1333–1357

Lagerklint M, J.D. Wright 1999 Late glacial warming prior to Heinrich event 1: The influence of ice rafting and large ice sheets on the timing of initial warming. Geology; December 1999; v. 27; no. 12; p. 1099–1102;

Reimer, P et al; 2004 IntCal04, Radiocarbon Volume 46, nr 3,

We should always remember that the energy arriving at the earth's surface varies considerably from equator to pole and is redistributed from equator to pole by various atmospheric and oceanic processes.

So is what you are saying is that the climatic variations over the past planet do not match present day distribution patterns?

For instance, if you want to contain the thermal energy at the lower lattitudes,

....(as well as much colder ones?)...

Did anybody follow that or do I have to translate?

See also the scientific method.

So my reading of it is that there is this seeming contradiction. Sea temperatures are getting colder, but at the same time the ice is retreating.

You seem to refute that it was actually getting colder.

First impression is that if the Younger Dryas is equally enigmatic, how can you endorse an meltwater rerouting hypothesis

Conversely, inferred meltwater flow to the Gulf of Mexico during the Mystery Interval does not support a simple routing event