Biomarker evidence for Arctic-region sea ice coverage in the northern Barents Sea indicates the most extensive sea ice conditions of the last 9,500 years occurred during the 20th century (0 cal yr BP).
In contrast, this region was ice-free with open water conditions during the Early Holocene (9,500-5,800 years ago).
Atlantic water inflow & sea ice distribution in the northern Barents Sea: A Holocene palaeoceanographic evolution
The early Holocene (ca. 9500 – 5800 cal yr BP) … Relatively low IP25 concentrations [a proxy for sea ice presence] with increased brassicasterol abundances indicate reduced seasonal (spring) sea ice cover and longer (warmer) summers with open water conditions suitable for phytoplankton production.
The occurrence of reduced sea ice cover and longer summers is consistent with increased planktic foraminiferal concentrations (reported here and Carstens et al., 1997) and with longer ice-free seasons and a retreated ice margin in the northern Barents Sea (Duplessy et al., 2001) as well as increased phytoplankton production in the northern Fram Strait (Müller et al., 2009).
Reduced spring sea ice cover also indicates the HTM recorded at the sea surface between ca. 9300 and 6500 cal yr BP, which probably results from maximum summer insolation at 78° N.”
Our proposed sea ice scenario suggests that water masses south of the study area were ice free, which agrees with open water conditions observed in the western Barents Sea (Berben et al., 2014) and the West Svalbard margin (Müller et al., 2012) during the early Holocene.
For the West Svalbard margin, Werner et al. (2013) associated high planktic foraminiferal fluxes ca. 8000 cal yr BP to ice-free or seasonally fluctuating sea ice margin conditions.
The PBIP25 index shows the lowest values of the record (0.16 – 0.40) suggesting a period characterized by low or variable seasonal sea ice cover and influenced substantially by open water conditions (Müller et al., 2011).
The late Holocene (ca. 2200 – 0 cal yr BP) is characterized by the highest abundances of IP25 (0.35 µg/g OC) and relatively low (but stable) brassicasterol (12.5 µg/g OC) (Figure 7A-B).).
Consistent with the opposing trends in the IP25 and brassicasterol records, the PBIP25 values reach their highest value (0.87) of the record at ca. 0 cal yr BP. An increase in PBIP25 suggests a further extension in sea ice cover, reflecting Arctic Front conditions (Müller et al., 2011), most similar to modern conditions.
The Early Holocene was about 6-7°C warmer than today in this region (NW Barents Sea).
Image Source: Tarasov et al., 2018
Another recent reconstruction for this region also indicated the Early Holocene was sea ice free and that modern sea ice conditions are among the most extensive of the last 9,500 years.
Image Source: Köseoğlu et al., 2018
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If the Arctic ice were all to melt, sea-levels would not be affected. You can prove this with a simple experiment you can do at home.
Take a jug, fill it half-full of warm water and put a large ice cube in the water. Mark on the jug the top level of the water. Now wait. The ice will melt, becoming water and will mix with the other water in the jug. Eventually, the ice cube will melt. Look at your mark. The water level won’t have changed. How come?
The answer is simple science. When an ice cube floats in water, 90% of it is under the water and 10% is above the waterline. To understand what happens next, remember that when water freezes, it expands. ( That’s why pipes burst when the water in them freezes. ) The opposite is also true: when ice melts, it contracts to a smaller amount of water. So the 90% of the ice cube under the water will actually lower the waterline as it melts.
Let’s not forget the 10% of the ice cube that’s above the waterline: when that melts, it contracts too. However, the melted ice – now water – adds to the water in the jug to bring the water level back to the mark on the jug. So, no change in the level.
But what if the Arctic ice were to melt completely? From our little experiment with the jug and the ice cube, we’ve seen that the sea level wouldn’t rise at all. The Northwest Passage would be permanently open to shipping, saving shipping lines massive amounts of time and money. The polar bears would migrate south and perhaps revert to being the black bears they once were. We’d have no more daft people trekking to the North Pole and getting frostbite; no intrepid sailors trying to sail to the North Pole and getting stuck in the ice half-way. Finally, the several nations who lay claim to the North Pole would see their flags floating away, removing a source of potential conflict. A win-win, I’d say.
Feedback in the climate system plays a big role in the climate.