From the section describing the mid-late Holocene [6900-1100 years before the present]:
"the sea ice biomarker IP25 is mainly absent throughout the mid-late Holocene, reﬂecting predominantly ice free ocean conditions (Fig. 7g–h)."From the section describing the late Holocene [1100-0 years before the present]:
"The sSST and δ185 O values might indicate a minor cooling in this period, however the mean values are only 5.7 ◦C and −0.23 % compared to 5.9 ◦C and −0.20 % in the preceding period (Fig. 7d–e). ... The fluctuating absence and presence of IP25 (at very low concentrations) and increasing brassicasterol 15 concentrations during the last [1100 years before the present] suggests that this area experienced sea ice conditions, with alternating periods of ice-free conditions and low occurrences of seasonal sea ice close to the core site (Fig. 7g–h). Such conditions are similar to those of the present day based on satellite imagery and biomarker reconstructions (Navarro-Rodriguez et al., 2013).
|Fig. 7. Seasonal sea ice extent shown in 2 graphs at far right increased over past ~1100 years in comparison to 6900-1100 years ago. Sea surface temperatures shown in 5th graph from the right show a "minor cooling."|
Clim. Past Discuss., 9, 4893-4938, 2013
1Department of Geology, University of Tromsø, 9037 Tromsø, Norway
2Biogeochemistry Research Centre, School of Geography, Earth and Environmental Sciences, University of Plymouth, Drake Circus, Plymouth PL4 8AA, UK
Abstract. In order to elucidate a continuous Holocene high resolution record of past variability of Atlantic water inflow and sea ice distribution, we investigate in this study a marine sediment core (JM09-KA11-GC) from the Kveithola Trough, western Barents Sea margin which is influenced by the north flowing North Atlantic Current (NAC).
The depth-age model for JM09-KA11-GC was constructed from 9 14C AMS dates and shows sediment accumulation rates from 0.04 to 0.67 mm yr−1, enabling a sub centennial resolution for most of the core. Planktic foraminifera, stable isotopes and biomarkers from sea ice diatoms and phytoplankton were analysed in order to reconstruct subsurface temperatures and sea ice distribution.
Throughout the early part of the Holocene (11 900–6900 cal yr BP), the foraminiferal fauna is dominated by the polar Neogloboquadrina pachyderma (sinistral) and the biomarkers show an influence of seasonal sea ice. Between 11 300 and 11 100 cal yr BP, a clear cooling is shown both by fauna and stable isotope data corresponding to the so-called Preboreal Oscillation. After 6900 cal yr BP the subpolarTurborotalita quinqueloba becomes the most frequent species, reflecting a stable Atlantic water inflow. Subsurface temperatures reach 6 °C and biomarker content indicates open water with mainly ice-free conditions. During the last 1100 cal yr BP, biomarker abundances and distributions show the re-appearance of low frequency seasonal sea ice and the planktic fauna show a reduced salinity in the subsurface water. No apparent temperature decrease is observed during this interval, but the rapidly fluctuating fauna and biomarker distributions indicate more unstable conditions
We know what caused the Barentsz Sea to be ice-free back then. It is not what is causing it to be ice-free now. So what is causing it to be as ice-free as back then?ReplyDelete
Of course, it's good to remember that the Barentsz Sea is on the outer fringe of the ice pack. However, as we speak, the ice edge on the Atlantic side of the ice pack (in the Barentsz corner) has retreated almost up to 85°N, and could go even as far as 87°N under the right conditions in the next two-three weeks, if it gets connected to a large hole in the interior of the ice pack.
This is something that probably has happened as well during the Holocene Climatic Optimum, but this time it's not the tilt of Earth's axis that is causing it. So, again, what is?
"We know what caused the Barentsz Sea to be ice-free back then. It is not what is causing it to be ice-free now."Delete
Where is the proof of that?
There is MORE seasonal sea ice today than during most of the Holocene from 6900-1100 years ago, according to the paper.