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Guest review article by David Middleton

We’re often bombarded with headlines line this:

Arctic sea ice continues its downward spiral

At 4.6 million square kilometres in coverage, this year’s sea ice minimum is the sixth lowest on record.

The problem with headlines like this is the fact that the “record” only dates back to 1979. How meaningful could “the sixth lowest on record” be, when the record isn’t even forty years long?

NSIDC does feature an estimate of Arctic sea ice extent that goes back to 1953 based on the “Hadley data set”…

Arctic sea ice before satellites, NSIDC

Based on this analysis, Arctic sea ice extent was anomalously high from 1953 to 1978 and has shrunk to anomalously low since 1979.  This is not very meaningful from a geological perspective.  In a previous post, I cited McKay et al., 2008 as an example of a geological perspective on Arctic sea ice extent.

The Arctic was probably ice-free during summer for most of the Holocene up until about 1,000 years ago.  McKay et al., 2008 demonstrated that the modern Arctic sea ice cover is anomalously high and the Arctic summer sea surface temperature is anomalously low relative to the rest of the Holocene.

chukchichukchi

“Modern sea-ice cover in the study area, expressed here as the number of months/year with >50% coverage, averages 10.6 ±1.2 months/year… Present day SST and SSS in August are 1.1 ± 2.4 8C and 28.5 ±1.3, respectively… In the Holocene record of core HLY0501-05, sea-ice cover has ranged between 5.5 and 9 months/year, summer SSS has varied between 22 and 30, and summer SST has ranged from 3 to 7.5 8C (Fig. 7). (McKay et al., 2008)

Over most of the Holocene, >50% sea ice coverage occurred from 5.5 to 9 months each year.  During the “Anthropocene”, >50% sea ice coverage has ranged from 9 to 12 months each year.

AnthropoceneAnthropocene

Yes… I know there are only 12 months in a year.

Steve Mosher noted in the comments that, “The Chukchi Sea IS NOT THE ARCTIC !!!! It is part of the arctic.”

This is very true… However, sediment cores are pretty-well limited to where they have been drilled.   In another recent thread, tty brought Stein et al., 2017 to my attention.  After reading through it, I decided that there was enough material there to take a crack at a general characterization of Holocene sea ice conditions relative to modern times.

PIP25: “Miracle on Ice”

In a pioneering study by Belt et al. (2007), the ability to (semi-)quantitatively reconstruct paleo-sea ice distributions has been significantly improved by a biomarker approach based on determination of a highly branched isoprenoid (HBI) with 25 carbons (C25 HBI monoene = IP25). This biomarker is only biosynthesized by specific diatoms living within the Arctic sea ice (Brown et al., 2014) and appears to be a specific, sensitive and stable proxy for Arctic sea ice in sedimentary sections representing Late Miocene to Recent times (Stein et al., 2012, 2016; Belt and M€uller, 2013; Stein and Fahl, 2013; Knies et al., 2014). The presence of IP25 in the studied sediments is direct evidence for the presence of sea ice.

[…]

For more semi-quantitative estimates of present and past sea ice coverage, M€uller et al. (2011) combined the sea-ice proxy IP25 and phytoplankton biomarkers in a phytoplankton- IP25 index, the so-called ‘PIP25 index’:

PIP25 = IP25/([IP25/(IP25 + ([phytoplankton marker] x c))

with c is the mean IP25 concentration/mean phytoplankton biomarker concentration for a specific data set or core.

[…]

Stein et al., 2017

The image below is of a Late Quaternary sea ice reconstruction for the western Yermak Plateau from Belt, et al., 2016

Pages from Belt_2013-2Pages from Belt_2013-2

Figure 6 from Belt et al., 2016. P8IP25 values for core PS2837-5 (western Yermak Plateau; after Stein et al., 2012) calculated from IP25 and brassicasterol data. Light to dark blue shadings indicate different degrees of sea ice cover (right). Dashed lines depict permanently ice covered intervals causing a lack of IP25 and brassicasterol, which hinders a calculation of the PBIP25 index. Red ellipse refers to the Intra-Allerød or Younger Dryas cooling, which is not properly displayed by the PBIP25 index. (Adapted from Stein et al., 2012).

Generally speaking, the PIP25 index correlates to sea ice extent as follows:

  • >0.7 = Perennial (year-round) ice cover
  • 0.5-0.7 = Seasonal ice cover
  • 0.1-0.3 = Reduced ice cover
  • <0.1 = Ice-free year-round

Most of the Arctic has had seasonal sea ice cover over the past 30 years, with a relatively small area of perennial sea ice.

Perennial sea ice is roughly equivalent to the recent minima.  Seasonal sea ice is more or less the difference between the maxima and minima.

So… How does this compare to the rest of the Holocene?

A geological perspective on Arctic sea ice extent

Kinnard et al., 2008 estimated Arctic sea ice extent minima and maxima back to about 1880 from a variety of methods.  A comparison of this with a PIP25 reconstruction of the North Icelandic Shelf sea ice extent suggests that modern sea ice extent is somewhere between that of the Little Ice Age (LIA) and Medieval Warm Period (MWP), probably closer to the MWP.

MWP_PresentMWP_Present

Figure 2a from Polyak et al., 2010 (originally from Kinnard et al., 2008) “Maximal (winter) and minimal (summer) Arctics ea-ice extent time series,1870–2003 (from Kinnard et al.,2008). Smooth lines are robust spline functions that highlight low-frequency changes.” Figure 4 from Belt et al., 2013: “Relative abundances of IP25 found in the core MD99-2275 for the period 800-1950 AD plotted against historical records of Icelandic sea ice interpreted from Ogilvie (1992) and Ogilvie and Jónsson (2001) (bottom scales) and diatom-based reconstructed sea surface temperature (Jiang et al., 2005) (Reproduced from Massé et al., 2008).”

Stein et al., 2017 compared sea ice extent reconstructions using PIP25 indices from four cores around the current area of perennial sea ice.

Stein_2017_MapStein_2017_Map

Figure 2 from Stein et al., 2017. Core locations relative to 2015 Arctic sea ice maximum and minimum extent.

A comparison of the Fram Strait core to the North Icelandic Shelf indicates that the sea ice extent of the MWP was anomalously higher than the vast majority of the Holocene.  Prior to the onset of Neoglaciation, Arctic sea ice extent appears to have ranged from nearly ice-free to the low end of seasonal coverage.

Holocene_MWPHolocene_MWP

Figure 4 from Belt et al., 2013 and figure 10 from Stein et al., 2017 (cropped). 

Andy May’s Arctic climate reconstruction exhibits the same general pattern as the four PIP25 sea ice extent reconstructions:

PiP25_May_ReconPiP25_May_Recon

Figures 10 and 6 from Stein et al., 2017 and Andy May’s Arctic climate reconstruction.

Prior to the onset of Neoglaciation, Arctic sea ice ranged from nearly ice-free to reduced.  Since the onset of Neoglaciation, it has ranged from seasonal to perennial.

I plotted Andy May’s excellent Arctic climate reconstruction as an overlay of the Chukchi Sea core from Stein et al, 2017 to demonstrate the relatively decent correlation between Arctic temperatures and sea ice conditions.  Note that all four core locations exhibit perennial sea ice during the Late LIA… And only during the Late LIA.

PiP25_May_Recon_2PiP25_May_Recon_2

Figure 10 from Stein et al, 2017 (orange stippled curve indicates insolation) and Andy May’s Arctic climate reconstruction.

While it is clear that Arctic sea ice extent has diminished since 1979, it’s also important to note that this reduction must be viewed in the context of the overall Holocene.  Holocene Arctic sea ice extent reached its Holocene maximum between 1600 and 1850 AD.

Figure 4 from Belt et al., 2013

So any reductions are from the maximum values of this geologic epoch.  The LIA was clearly the coldest phase of the Holocene and modern sea ice conditions are much closer to the LIA than they are to the pre-Neoglaciation period.

References

Alley, R.B. 2000.  The Younger Dryas cold interval as viewed from central Greenland.
Quaternary Science Reviews 19:213-226.

Belt S.T., Müller J.  The Arctic sea ice biomarker IP25: A review of current understanding, recommendations for future research and applications in palaeo sea ice reconstructions. (2013)  Quaternary Science Reviews,  79 , pp. 9-25.

Belt_2013

Hoff U, Rasmussen TL, Stein R, Ezat MM, Fahl K. Sea ice and millennial-scale climate variability in the Nordic seas 90 kyr ago to present. Nature Communications. 2016;7:12247. doi:10.1038/ncomms12247.

Hoff_2016

Kinnard, C., Zdanowicz,C.M., Koerner,R .,Fisher,D.A., 2008. A changing Arctic seasonal ice zone–observations from 1870–2003 and possible oceanographic consequences. 35, L02507.

Kinnard_2008

May, Andy. A Holocene Temperature Reconstruction Part 4: The global reconstruction. Watts Up With That. 2017.

May_2017

Polyak, Leonid, Richard B. Alley, John T. Andrews, Julie Brigham-Grette, Thomas M. Cronin, Dennis A. Darby, Arthur S. Dyke, Joan J. Fitzpatrick, Svend Funder, Marika Holland, Anne E. Jennings, Gifford H. Miller, Matt O’Regan, James Savelle, Mark Serreze, Kristen St. John, James W.C. White, Eric Wolff.  History of sea ice in the Arctic, Quaternary Science Reviews, Volume 29, Issues 15–16, 2010, Pages 1757-1778, ISSN 0277-3791, https://ift.tt/2C3wNyM.

polyak_etal_seaice_QSR_10

Stein, R. , Fahl, K. , Schade, I. , Manerung, A. , Wassmuth, S. , Niessen, F. and Nam, S. (2017), Holocene variability in sea ice cover, primary production, and Pacific‐Water inflow and climate change in the Chukchi and East Siberian Seas (Arctic Ocean). J. Quaternary Sci., 32: 362-379. doi:10.1002/jqs.2929

stein2017

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