The last glacial cycle was characterized by substantial millennial-scale climate fluctuations, but the extent of any associated changes in global sea level (or, equivalently, ice volume) remains elusive. Highstands of sea level can be reconstructed from dated fossil coral reef terraces, and these data are complemented by a compilation of global sea-level estimates based on deep-sea oxygen isotope ratios at millennial-scale resolution or higher. Records based on oxygen isotopes, however, contain uncertainties in the range of +/-30 m, or +/-1 degrees C in deep sea temperature. Here we analyse oxygen isotope records from Red Sea sediment cores to reconstruct the history of water residence times in the Red Sea. We then use a hydraulic model of the water exchange between the Red Sea and the world ocean to derive the sill depth-and hence global sea level-over the past 470,000 years (470 kyr). Our reconstruction is accurate to within +/-12 m, and gives a centennial-scale resolution from 70 to 25 kyr before present. We find that sea-level changes of up to 35 m, at rates of up to 2 cm yr(-1), occurred, coincident with abrupt changes in climate.

This paper describes the fluid mechanics of the natural ventilation of a space connected to a large body of stationary ambient fluid. The flows are driven by buoyancy differences between the interior and exterior fluids. Connections with the ambient fluid are high level and low level openings. Two main forms of ventilation are identified : mixing ventilation and displacement ventilation. Mixing ventilation occurs when the incoming ambient fluid mixes with the fluid within the space, as is the case if dense fluid enters through a high level inlet. In this case vertical stratification is weak. Displacement ventilation occurs when dense fluid enters at low levels and displaces the lighter fluid within the space out through high level openings. A strong stable Stratification develops in this case, and there is little mixing between the incoming fluid and that in the interior. Both of these modes of ventilation are studied theoretically and the results are compared with laboratory experiments. Transient draining flows which occur when a space initially contains fluid of a density different from the ambient are examined. The presence of internal sources of buoyancy allows steady states to be established, and the effects of point, line and vertically distributed sources are studied. Thesc steady states are extensions of filling box models, with the addition of continuous exchange of fluid with the environment outside the space. A major result of this work is that the form of the stratification within the space depends on the entrainment caused by the convective elements (plumes) produced by the buoyancy sourcesiJbut is independent of the strength of the sources. The strength of the stratification and the magnitudes of the velocities do, however, depend on the source strength. The effects of opening size(s) and configurations are determined, and criteria for producing a particular stratification within the space are established. Applications of this work to the ventilation of buildings are presented.

Highlights 22• The RAPID moorings array is measuring the AMOC at 26.5ºN continuously since 23 24• The AMOC has a strength of 17.2 Sv and heat transport of 1.22 PW over the 8. • Improved estimation of the shallowest and deepest transports 27• Changes to the calculation have reduced the estimate of the AMOC by 0.6 Sv 28

The Atlantic Meridional Overturning Circulation (AMOC) is responsible for a variable and climatically important northward transport of heat. Using data from an array of instruments that span the Atlantic at 26°N, we show that the AMOC has been in a state of reduced overturning since 2008 as compared to 2004–2008. This change of AMOC state is concurrent with other changes in the North Atlantic such as a northward shift and broadening of the Gulf Stream and altered patterns of heat content and sea surface temperature. These changes resemble the response to a declining AMOC predicted by coupled climate models. Concurrent changes in air‐sea fluxes close to the western boundary reveal that the changes in ocean heat transport and sea surface temperature have altered the pattern of ocean‐atmosphere heat exchange over the North Atlantic. These results provide strong observational evidence that the AMOC is a major factor in decadal‐scale variability of North Atlantic climate.

Ocean impact on decadal Atlantic climate variability revealed by sea-level observations. Nature, 521 (7553). 508-510. 10.1038/nature14491 Contact NOC NORA team at publications@noc.soton.ac.ukThe NERC and NOC trademarks and logos ('the Trademarks') are registered trademarks of NERC in the UK and other countries, and may not be used without the prior written consent of the Trademark owner. properties and offer timeseries of sufficient length (Ext. Data Fig. 1) to study decadal 46 ocean circulation variations. Investigating ocean circulation using tide gauges is not new: 47 the first attempt to estimate the Gulf Stream using tide gauges was made in 1938 14 . The 48 principle is based on geostrophic dynamics: on timescales longer than a few days, ocean 49 circulation is in geostrophic balance so, looking downstream, the sea level is seen to 50increase from left to right in the northern hemisphere. 51 52Estimates of the Gulf Stream using tide gauges have focused on the use of gauges on the 53American east coast with an offshore estimate of sea level from either an island gauge 15 54 or a reconstructed sea level 16 . A weakness of this method is that the offshore 55 measurement lies in the eddy-filled ocean where sea-level fluctuations at any one point 56 are influenced by the mesoscale 17 even on long timescales, increasing the difficulty of 57 making estimates of ocean circulation that is coherent on large spatial scales. This is the 58 case for sea level at Bermuda, whose decadal fluctuations can be reproduced by 59 considering a Rossby wave response to wind forcing 16 . To make estimates of ocean 60 circulation that capture the fluctuations in large-scale circulation and less eddy variability, 61 measurements close to or on the western boundary are necessary 18 . We account for this 62 by focusing on the gradient of sea level along the US east coast. The mean dynamic sea 63 level decreases to the north along the east coast of the US (Fig. 1a) (Fig. 1a), we can construct a single sea-level composite 82 representative of the subtropical (subpolar) circulation by averaging sea-level from 83 linearly detrended, deseasonalised tide gauges, with the inverse barometer effect removed, 84 south (north) of the Cape (Fig. 1b, c). The difference, south minus north (Fig. 1d), 85 represents our circulation index. This index projects onto observed surface velocities 86 during the satellite era in the intergyre region, with a positive index associated with more 87 northwards flow and a more northerly path of this circulation (Extended Data Fig. 4). captured by the accumulated sea-level index, observationally supporting the hypothesis 113 6 that circulation changes and not only air-sea fluxes were involved in these changes 28 . For 114 the purposes of statistical analyses, the timeseries have had a 7-year low-pass, Tukey 115 filter applied to them, which is referred to with the prefix '7-year' from here on. The 7-116 year sea-level index leads the 7-year rate of heat content change by 2 years with a 117 maximum correlation of ...

[1] The spatial distribution of turbulent dissipation rates and internal wavefield characteristics is analyzed across two contrasting regimes of the Antarctic Circumpolar Current (ACC), using microstructure and finestructure data collected as part of the Diapycnal and Isopycnal Mixing Experiment in the Southern Ocean (DIMES). Mid-depth turbulent dissipation rates are found to increase from O 1 Â 10in the Scotia Sea, typically reaching 3 Â 10 À9 W kg À1 within a kilometer of the seabed. Enhanced levels of turbulent mixing are associated with strong near-bottom flows, rough topography, and regions where the internal wavefield is found to have enhanced energy, a less-inertial frequency content and a dominance of upward propagating energy. These results strongly suggest that bottomgenerated internal waves play a major role in determining the spatial distribution of turbulent dissipation in the ACC. The energy flux associated with the bottom internal wave generation process is calculated using wave radiation theory, and found to vary between 0.8 mW m À2 in the Southeast Pacific and 14 mW m À2 in the Scotia Sea. Typically, 10%-30% of this energy is found to dissipate within 1 km of the seabed. Comparison between turbulent dissipation rates inferred from finestructure parameterizations and microstructurederived estimates suggests a significant departure from wave-wave interaction physics in the near-field of wave generation sites.

[1] The exchange between the Persian (Arabian) Gulf and the Indian Ocean is investigated using hydrographic and moored acoustic Doppler current profiler data from the Straits of Hormuz during the period December 1996 to March 1998. The moored time series records show a relatively steady deep outflow through the strait from 40 m to the bottom with a mean speed of approximately 20 cm/s. A variable flow is found in the upper layer with frequent reversals on timescales of several days to weeks. The annual mean flow in the near-surface layer is found to be northeastward (out of the Persian Gulf) in the southern part of the strait, suggesting a mean horizontal exchange with the Indian Ocean that is superimposed on the vertical overturning exchange driven by evaporation over the gulf. The salinity of the deep outflow varies from 39.3 to 40.8 psu with highest outflow salinities occurring in the winter months (December-March). The annual mean deep outflow through the strait is estimated to be 0.15 ± 0.03 Sv. Calculation of the associated heat and freshwater fluxes through the strait yields estimates for the annual heat loss over the surface of the gulf of À7 ± 4 W/m 2 and an annual water loss (E-P-R) of 1.68 ± 0.39 m/yr. These values are shown to be in relatively good agreement with climatological surface fluxes derived from the Southampton Oceanography Centre global flux climatology after known regional biases in the radiative budget are taken into account.

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