ephemeral formation of perennial sea ice in the arctic ocean … · 2014-02-27 · ellesmere island...

Supplementary Information: Ephemeral formation of perennial sea-ice in the Arctic Ocean

during the middle Eocene (~44 Ma)

Additional Comments on Drift Times

Drift distances are calculated from the 40 MA tectonic reconstruction of the Arctic Ocean

and are calculated from the approximate (±50 km) from the paleo-shoreline. Little is known of

the tectonic history of the shelves at this time, but because sea levels were generally higher than

today during the Eocene and most of the Pliocene, it may be safe to assume that the shelves were

submerged. The diminished distances resulting from assuming emerged shelves is negligible for

the most important North American sources such as the Banks Island area because of the narrow

shelves there.

When curvilinear drift paths are used that more closely approximate the Modern mean

drift field and assuming no changes in direction, all of the source shelf areas from northern

Ellesmere Island to the East Siberian Sea require more than a year for ice to reach the ACEX site

even using the faster drift rate of 5 cm/sec (0.8 yr. for most of the E. Siberian Sea, Table 1, Fig.

1) but only the Barents shelf is less than a year drift time using the Modern average drift rate of

3cm/sec. Even the simple curvilinear drift paths for today are net average drift paths because ice

drift changes direction frequently and on average it takes more than five years for ice to exit the

Beaufort Gyre and reach the ACEX core site (Rigor et al., 2002). Thus the drift paths used here

are highly conservative and are likely to under estimate perennial ice conditions.

Detailed Fe Grain Matches

While the maximum number of Fe grains matched to any one of the 41 source areas

shown in Fig. S1 is an unbiased representation of significant source contribution when five or

Ephemeral formation of perennial sea ice in the Arctic Ocean during the middle Eocene

SUPPLEMENTARY INFORMATIONDOI: 10.1038/NGEO2068

NATURE GEOSCIENCE | www.nature.com/naturegeoscience 1

© 2014 Macmillan Publishers Limited. All rights reserved.

http://www.nature.com/doifinder/10.1038/ngeo2068

more grains are matched, it does not show which of the 41 circum-Arctic sources contributed to

each ACEX core sample. All of the sources that had significant input to any ACEX sample are

shown in Fig. S2.

Fig. S1. Circum-Arctic source areas used to match Fe grains from the ACEX core (Darby et al.,

2012).

2 NATURE GEOSCIENCE | www.nature.com/naturegeoscience

SUPPLEMENTARY INFORMATION DOI: 10.1038/NGEO2068



Fig. S2. Total Fe grains from each source area with five or more grains matched. The source

area (SA) numbers shown below each plot correspond to the numbered source areas in Fig. S1.

Note that the source areas with the largest number of maximum Fe grains matched are northern

Ellesmere Island and Banks Island, both require more than five years drift to reach the ACEX

site today (Rigor et al., 2002).

4 NATURE GEOSCIENCE | www.nature.com/naturegeoscience

SUPPLEMENTARY INFORMATION DOI: 10.1038/NGEO2068



References

Darby, D.A., Ortiz, J.D., Grosch, C.E., Lund, S.P., 1,500-year cycle in the Arctic Oscillation

identified in Holocene Arctic sea-ice drift. Nature Geoscience, 5, 897-900 (2012).

Rigor, I. G., Wallace, J. M., and Colony, R. L., Response of Sea Ice to the Arctic Oscillation.

Jour. of Climate, 15, 2648-2663 (2002).





ephemeral formation of perennial sea ice in the arctic ocean … · 2014-02-27 · ellesmere island...

Documents