V9 Antarctic Peninsula_Voyage_Log

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When and How the Earth Got Cold David Macdonald, Leturer (Geology) & Expedition Guide The Earth’s climate has two end-member states: greenhouse and icehouse. In a greenhouse climate, there are no polar icecaps (although there may be valley glaciers in high mountain areas) – the climate of the Cretaceous Period (144-65 million years ago) is a typical greenhouse. We are currently in an icehouse climate, since there are icecaps at or near both poles. Although life on Earth goes back 3.5 billion years, the main expansion in numbers of species and hence of easily found fossils occurred 540 million years ago. During the time from then until now, greenhouse climates have dominated, with three periods of icehouse climate, lasting a total of about 100 million years. Our current icehouse period began abruptly 35 million years ago, with formation of an icecap in Antarctica. Why did it happen then, and why did it have such an abrupt beginning? Water temperature (°C) Antarctic convergence October 2019 8 6 4 2 0 54 56 58 60 62 64 Latitude (°S) 17 Figure 2: Temperatures in the Drake Passage from Friday 25 October to Sunday 27 October 2019 as Ocean Atlantic sailed south across the Antarctic Convergence, where the sea temperature falls below 4°C. It was the severing of the link between the Antarctic Peninsula and Tierra del Fuego that allowed deep cold water to circulate around the planet at 50-60°S and thermally isolate Antarctica from the rest of the world. This situation continues today (Figure 1) The key area for this was the Drake Passage, which is the western end of the Scotia Sea (Figure 3). Geological and geophysical studies of the sea floor show that the Antarctica-South America link was severed by the growth of ocean crust, beginning 35 million years ago. Opening of this deep-water gateway cooled the planet and turned Antarctica into the white continent. Figure 1: Thermal structure of the Southern Ocean showing the position of the Antarctic Convergence (Polar Front) at the junction of the dark blue and mid blue shading. This is the line of the 4°C isotherm, where Antarctic surface water plunges below cold temperate water. The first, and most important factor was that we had a polar continent. Antarctica was in roughly its present position over the South Pole, so would have had strongly differentiated winters and summers. However, although the former supercontinent of Gondwana had largely broken up by then, there was still a land bridge to South America and Antarctica was still forested, probably with a migratory fauna. Warm currents bathed Antarctica’s shores and, 35 million years ago, the temperature of the Southern Ocean was a relatively mild 6°C. 5 JAN 2020 – 14 JAN 2020 Figure 3: The Drake Passage and the Scotia Sea formed from 50 million years ago, when there was slow extension between South America and the Antarctic Peninsula which stretched the crust and allowed surface waters to circulate through this former land bridge. The temperature of the southern Ocean fell from 12°C to 6°C between 50-35 million years ago, then abruptly fell to 0°C when the deep water gateway of the scotia Sea opened, sundering the link between Antarctica and South America and allowing continuous circulation of deep water, thermally isolating Antarctica. Volume 2, Issue 9
© Renato Granieri 5 JAN 2020 – 14 JAN 2020 Volume 2, 2, Issue 98
Page 1 and 2: 5 JAN 2020 - 14 JAN 2020 Albatros M
Page 3 and 4: TABLE OF CONTENTS The Voyage Meet t
Page 5 and 6: Meet the Team 4 Phil Hunter Assista
Page 7 and 8: The Seven Sisters of Szczecin David
Page 9 and 10: Rolling Our Way South 6 January 202
Page 11 and 12: Approaching the ice 7 January 2020
Page 13 and 14: Drake Passage 5 JAN 2020 - 14 JAN 2
Page 15 and 16: Chasing Icebergs, Finding Penguins
Page 17: The White Continent 9 January 2020
Page 21 and 22: Deception Island 11 January 2020- B
Page 23 and 24: A Brief History of the Zodiac Steve
Page 25 and 26: Northward Bound 12 January 2020- Dr
Page 27 and 28: Towards the Horn 13 January 2020- D
Page 29 and 30: King of the Southern Winds Sandra O
Page 31 and 32: By the Numbers… 30 Voyage Statist

V9 Antarctic Peninsula_Voyage_Log

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