Hydrosphere – Physical basis of climate spring 2011 Global temperatures Density seawater Mixed layer – thermocline Abyssal circulation Antarctic Circumpolar current Ekman spiral Abrupt climate change Much material and some figures from http://oceanworld.tamu.edu/resources/ocng_textbook/contents.html

ρ = ρ(T) ρ1 = ρ0 / (1 + β (t1 - t0))  Β(T) = volumetric temperature expansion coefficient (K-1) = 0.0002 water at 20°C. ρ = ρ(p) ρ1 = ρ0 / (1 - (p1 - p0) / E) E = bulk modulus fluid elasticity (N/m2) = 2.15e9 (N/m2) water.

Density = 10275 kg/m3 Figure 6.9 Profiles of Left in situ and potential temperature and Right sigma-t and sigma-theta in the Kermadec Trench in the Pacific measured by the R/V Eltanin during the Scorpio Expedition on 13 July 1967 at 175.825°E and 28.258°S. Data from Warren (1973).

Seawater Equation of State Curry and Webster, pp21 ρ(T, S, p) = ρ(T, S, 0)/ [1-KT(T, S, p)] KT ≡ mean bulk modulus α (compressibility)-1 ρ(T, S, 0) = a + b S + c S3/2 + d S2 KT(T, S, p) = e + f S + g S3/2 + (h + i S + j S3/2) p + (m + n S) p2 a - n = f(∑ ai Ti, i=0,5) Density of seawater not measured but calculated form equation of state after measuring, T, S, and p.

Epipelagic = Euphotic or sunlit zone

Figure 5.11 Northward heat transport for 1988 in each ocean and the total transport summed over all oceans calculated by the residual method using atmospheric heat transport from ECMWF and top of the atmosphere heat fluxes from the Earth Radiation Budget Experiment satellite.

Figure 13.10 Contour plot of salinity as a function of depth in the western basins of the Atlantic from the Arctic Ocean to Antarctica. The plot clearly shows extensive cores, one at depths near 1000m extending from 50°S to 20°N, the other at is at depths near 2000m extending from 20°N to 50°S. The upper is the Antarctic Intermediate Water, the lower is the North Atlantic Deep Water. The arrows mark the assumed direction of the flow in the cores. The Antarctic Bottom Water fills the deepest levels from 50°S to 30°N. See also Figure 6.11. From Lynn and Reid (1968). Figure 10.15 Distribution of tritium along a section through the western basins in the North Atlantic.

Figure 13.1 The surface (red, orange, yellow) and deep (violet, blue, green) currents in the North Atlantic.

Ekman Spiral – Northern Hemisphere

Figure 13.12 Cross section of neutral density across the Antarctic Circumpolar Current in the Drake Passage from the World Ocean Circulation Experiment section A21 in 1990. The current has three streams associated with the three fronts (dark shading): SF = Southern acc Front, PF = Polar Front, and SAF = Subantarctic Front. Hydrographic station numbers are given at the top, and transports are relative to 3,000dbar. Circumpolar deep water is indicated by light shading. From Orsi (2000).

Figure 13.13 Distribution of the Subantarctic and Polar Fronts and associated currents in the Antarctic. From Whitworth (1988). SF = Southern acc Front, PF = Polar Front, and SAF = Subantarctic Front.

Figure 4. (Top) The δ18O record from the GISP2 ice core in Greenland, showing 20 of the 25 observed Dansgaard-Oeschger events during the last glacial period (Grootes et al., 1993). (Bottom) A record of ice-rafted material during Heinrich events from a deep-sea core in the North Atlantic (Bond and Lotti, 1995).

Paleoclimatic data showing abrupt climate changes, after (45) and other sources. The lower panel is the history of temperature in central Greenland over the last 110,000 years (72). Details of temperature for the Younger Dryas (YD) event and for the cold event about 8200 years ago (8ka) are shown as deviations from the temperature averaged over the intervals from 7000 to 8000 and 8400 to 9000 years ago. Methane concentrations (23) reflect production in global wetlands, including important tropical sources. Gray-scale of a sediment core from the Cariaco Basin, offshore Venezuela (73), is plotted here so that a downward shift corresponds to the effects of stronger winds over the basin or decreased rainfall on adjacent land. Note differences in scales in the detailed figures; the scale for the Cariaco Basin record is not shown, but has twice the range for the YD as for the 8ka. Figure 3 Paleoclimatic data showing abrupt climate changes, after (45) and other sources. Published by AAAS R B Alley et al. Science 2003;299:2005-2010

End of the last glacial period 11,500 years ago End of the last glacial period 11,500 years ago. Earth's climate system began to look like it does today. Large continental ice sheets shrank, sea level rose, temperatures ameliorated, monsoons grew in strength. Around 8,200 years ago, however, a surprising event was discovered in the Greenland ice core GISP2. Over two decades temperature cooled about 3.3°C in Greenland (Alley et al., 1997; Kobashi et al., 2007). The entire event lasted about 150 years. Cause draining of Lake Agassiz? Further evidence of ice dams breaking leading to massive flooding first proposed by Bretz in early 1900s.

Younger Dryas