FRESH WATER AS AN ESSENTIAL CLIMATE VARIABLE

Transcription

1 FRESH WATER AS AN ESSENTIAL CLIMATE VARIABLE IN THE ARCTIC CLIMATE SYSTEM Dmitry Dukhovskoy Center for Ocean-Atmospheric Prediction Studies, Florida State University, USA Andrey Proshutinsky Woods Hole Oceanographic Institution, USA Mary-Louise Timmermans Yale University, USA Jonathan Bamber University of Bristol, UK BthC Beth Curry University of Washington, USA Raquel Somavilla Instituto Español de Oceanografia, Spain Mark Bourassa Florida State University, USA Acknowledgments: Presented results are from several research projects funded by the NSF, NASA Ocean Vector Winds Science Team, Office of Naval Research. Picture: Greenland Glacier, from the National Geographic

2 Fresh Water and Ocean Essential Climate Variables Sea Surface Height 3D Temperature Fields 3D Salinity Fields 3D Current Fields Nutrients Carbon Ocean Tracers Phytoplankton Fresh Water Content FWC z S ref S ref S( z) dz S Change of the Sea Ice Volume River runoff P-E Ice Sheet Discharge Oceanic FW fluxes (Bering Strait, Canadian Arctic Archipelago, Fram Strait) ref Freshwater Fluxes:

3 Arctic Ocean as an Estuary An estuary is a semi-enclosed enclosed coastal body of water which has a free connexion with the open sea and within which sea water is measurably diluted with fresh water derived from land drainage. Cameron and Pritchard, 1963, Estuaries. Oceanic freshwater storage (S ref =34.8) Liquid: 74000±7400 km 3 Propagation of the GSA 1970s Sea ice: km 3 Propagation of the GSA CAA: 1980s Liquid: km 3 /yr Belkin et al., 1998 Ice: -160 km 3 /yr Total freshwater inflow: ~8090 km 3 /yr Rivers: 3200±110 km 3 /yr P-E: 2000±200 km 3 /yr Bering Strait (liquid) 2500±300 km 3 /yr Bering Strait (ice) 140±40 km 3 /yr Norwegian Current 250±50 km 3 /yr Serreze et al., Belkin et al., 1998 Belkin, 2004 Fram Strait: Liquid: km 3 /yr Ice: km 3 /yr Source: Arctic Great River Observatory

4 Beaufort Gyre as a Freshwater Reservoir More than half of the total Arctic Ocean s liquid fresh water is stored in the Canada Basin with the Beaufort Gyre containing >20, km 3 of liquid fresh water (Aagaard and Carmack, 1989). Freshwater Content (m) S ref = 34.8, from the GDEM climatology The volume of freshwater in the Beaufort Gyre is close to the volume of fresh water in Lake Baikal, Siberia (23,000 km 3 ), the largest freshwater lake by volume in the world and is comparable with fresh water volume stored in all Great Lakes (23,000 km 3 ). The Beaufort Gyre freshwater volume is >5 times larger than the total annual river runoff to the Arctic Ocean and approximately 2 times larger than the volume of fresh water stored in Arctic sea ice.

5 ARCTIC OCEAN OSCILLATION (AOO) Mean Sea Level Pressure and Geostrophic Winds over Sea Level Pressure, Ice Drift, and Cyclone Tracks during Cyclonic and danticyclonic i Circulation i Regimes Arctic Oscillation Index, Anticyclonic Regime NCEP/NCAR reanalysis data provided by the NOAA/OAR/ESRL/PSD Boulder, CO, USA Cyclonic Regime Proshutinsky and Johnson, 1997; Proshutinsky et al., 2015

6 ARCTIC OCEAN - NORTH ATLANTIC AUTO-OSCILLATORY SYSTEM Dukhovskoy et al., 2006 Sub-Arctic Seas More detail in: Dukhovskoy et al., GRL, 2004; JGR, 2006

7 CESSATION OF DECADAL ARCTIC CLIMATE VARIABILITY IN THE 2000S Arctic Ocean Oscillation (AOO) 19 years 19 years of Anticyclonic Circulation Regime

8 Why has the well-pronounced Arctic decadal variability observed in the 20 th century been replaced by relatively weak interannual changes under Anticyclonic Circulation Regime conditions in the 21 st century?

9 Changes in the Arctic Ocean Freshwater Budget Changes in the 2000s compared to (x10 3 km 3 ): Liquid FW (93 101): +9% Beaufort Gyre ( ): +34% Multiyear ice ( ): -33% Seasonal ice ( ): +3% Arctic sea ice on September 11, 2015 and the 36-year average minimum sea ice extent Fluxes (x10 3 km 3 /yr): P-E (2 2.2): +10% Runoff ( ): +8% Bering FW ( ): +4% Haine et al., 2015; Shiklomanov, 2010; Woodgate et al., 2012; Proshutinsky et al., Distribution of the Arctic Sea Ice Age in 1985 and 2015 Credits: NASA/Goddard Scientific Visualization Studio X10 6 km Discharge of Eurasian and North American Rivers No ice <1 yr 1-2 yrs 3-4 yrs >4 yr Perovich et al., Arctic Report Card: Update for Holmes et al., Arctic Report Card: Update for 2015.

10 CHANGES IN THE FRESHWATER TRANSPORTS TO THE NORTH ATLANTIC Haine et al., 2015 The most striking feature of the time series of East Greenland Current liquid freshwater fluxes observed by the Fram Strait moorings is that the annual mean flux does not show any large variations since Mauritzen et al., 2011; de Steur et al., 2009

11 Change of the Beaufort Gyre Freshwater Content during (from the BGOS observational records) The amount of surplus fresh water accumulatedinthe Beaufort Gyre over the 2000s can potentially impact the climate. Released to the sub-arctic seas, fresh water may inhibit deep convection there influencing the intensity of the ocean meridional overturning circulation and leading to climate cooling. Freshwater Content ( x 10 3 km 3 ), relative to S=34.8

12 Greenland Freshwater Flux Total Greenland FW flux: ~900 km 3 /yr in 1990 ~1100 km 3 /yr in % of the total runoff into the Arctic Ocean Greenland Freshwater Sources (km 3 /mo) July, 2006 Cumulative FW Anomalies (relative to ) for the 5 oceanic sectors and for the whole of Greenland (dashed black line) The volume of the surplus freshwater flux is ~1/2 of the 1970s Great Salinity Anomaly Whole Greenland Bamber et al., 2012, updated Dukhovskoy et al., JGR, 2016

13 HYPOTHESIS Additional freshwater fluxes into the sub-arctic seas, associated with the acceleration of Greenland ice sheet melt in the 21 st century, could be the major factor responsible for the cessation of decadal Arctic climate variability and stabilization of the present anticyclonic circulation regime over the Arctic Ocean.

14 Model Study of Greenland Freshwater Pathways in the sub-arctic Seas A model experiment with fully-coupled 0.08 HYbrid Coordinate Ocean Model (HYCOM) Los Alamos Sea Ice Model (CICE) of the Arctic Ocean Passive tracers are constantly released at the freshwater sources along the Greenland coast Freshwater Tracer Concentration (kg/m 3 ) for Selected Model Years Year 1 Year 5 Year 10 Year Estimated Salinity Change in the upper 400m for Time-Integrated Anomaly of Greenland Freshwater Flux for Iceland Sea Labrador Sea Greenland Sea Dukhovskoy et al., JGR, 2016

15 CC NASA-NOAA 2015 GLOBAL TEMPERATURE ANOMALY Relative to mean temperature NSA/GSFC/Scientific Visualization Studio

16 Summary Observational data reveal 9% increase of liquid FW in the Arctic Ocean (compared to ). = However, FWexport to the North Atlantic does not show large variations in the 2000s. Most of the surplus FW is accumulated in the Beaufort Gyre (+34% ) = Due to Anticyclonic Circulation Regime that has been dominated the Arctic since FW discharge from the Greenland Ice Sheet has been accelerating since = By now, the cumulative FW flux anomaly to the North Atlantic is ~ 5000 km 3. This excess Greenland FW may have significant impact to deep convection in the sub-arctic seas with subsequent atmospheric cooling. = The effect would be to impede the decadal oscillations that were a feature of the observations prior to the 2000s. The amount of surplus FW accumulated in the Beaufort Gyre over the 2000s (~6000 km 3 ) can impact the climate. = Released to the sub-arctic seas, fresh water may inhibit deep convection there influencing the intensity of the ocean meridional overturning circulation and leading to climate cooling.

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18 Sea Level Pressure Surface and Upper Air Temperature Geopotential Chukchi East- Heights Clouds Sea Siberian Vapor Sea Precipitation Laptev Beaufort Surface and Upper Sea Air Winds Sea Atmosphere Kara Sea Thickness Age Concentration Extent/Area Albedo Melt Ponds Drift Baffin Bay Davis Strait Labrador Sea Ice Denmark Strait Fram Strait Nordic Seas Barents Sea Fresh Water Content Subpolar Sref S( z) FWC dz Gyre z Sref S ref Ocean Sea Surface Height 3D Temperature Fields 3D Salinity Fields 3D Current Fields Waves Chemistry Biology

19 Greenland Freshwater Tracer Experiment HYCOM/CICE Modeling System of the Arctic Ocean Local Runoff Tracer Concentration ti Relaxation Time Scale (1 day) ARCc0.08: Coupled HYbrid Coordinate Ocean Model and Los Alamos Sea Ice Model (CICE 4.0) 32 hybrid vertical ocean layers Atlantic and Pacific Boundaries at ~39 N Closed in CICE Tracer Density Nested into 1/12 Global HYCOM (1000 kg/m 3 ) Initialized from a simulation with no Greenland runoff Currently run for 14 years Monthly Greenland runoff (Bamber et al., 2013) CFSR radiative fluxes Scatterometer based winds (CCMP) Passive tracers are constantly added at every runoff location. The tracer flux is proportional to the individual runoff at every location.

20 Year2 Year 3 Year 4 Year 5 Year 6 Year 7 Year 8 Year 9 Year 10 Year 11 Year 12 Year 13 Year 14 Year Tracer concentration (kg/m3)

21 CC 2 Winter (DJF) Latent Heat Flux (OAFlux, WHOI) Integrated over the Labrador and Nordic seas and Subpolar Gyre NASA-NOAA 2015 GLOBAL TEMPERATURE ANOMALY Labrador Relative to mean temperature 1 0 Subpolar Nordic Winter (DJF) Sensible Heat Flux (OAFlux, WHOI) Labrador Sea North Atlantic Nordic Seas NSA/GSFC/Scientific Visualization Studio

22 Labrador Sea Nordic Seas AIR-SEA HEAT FLUXES North Atlantic

23 NEAR-SURFACE SALINITY IN THE ICELAND AND GREENLAND SEAS From hydrographic hi measurements in (ICES and Pangaea Databases) Greenland Sea GSA70 GSA80 GSA90 Iceland Sea Dukhovskoy et al., 2016

24 Monthly salinity anomalies relative to Baffin Bay Monthly salinity anomalies derived from the Met Office Hadley Centre subsurface ocean salinity data set Salinity anomaly in Davis Strait relative to mean Mean S in Davis Strait ( ) Arctic Water West Greenland Shelf Water West Greenland Transient Iintermediate Water Water Mean S and anomalies derived from Davis Strait mooring observations (UW) Curry et al., 2014; Dukhovskoy et al., JGR, 2016

25 Salinization of the North Atlantic Current in the 2000s Holliday et al., GRL, 2008

26 Subtropical Signal Hatún et al., Science, 2005

27 BGOS: multi-institutional/disciplinary institutional/disciplinary logistics/platform

28 Bering Strait Locations Moorings of Meteorological (UW) 2000-present Monitoring Stations 3 moorings in the US waters: ADCP T/S Sea ice velocity and thickness Beaufort Sea Chukchi Sea East- Siberian Sea Laptev Sea Atmosphere NABOS/CABOS observations (IARC, UAF, NRL): 2003-present Moorings with ADCP/ULS/CTD chain, MMP profiler Ice-tethered profilers Meteorological buoys Shipboard surveys Beaufort Gyre Observing System (WHOI): 2003-present 4 moorings with upward-looking sonars, McLane Moored profiler, bottom pressure recorder Ice-tethered profilers Shipboard hydrographic surveys Davis Strait Full-depth Moorings and Seaglider surveys (UW) 2004-present ADCP T/S Baffin Bay Davis Strait Labrador Sea Ice Denmark OWS M (Mike) Strait (DNMI / EuroSITES / UiB) 1948-present Weather Subpolar ship until 2009, replaced by a mooring T/S/U Gyre Fram Strait Nordic Seas VEINS/ ASOF/ DAMOCLES moorings Kara Fram Strait (AWI, IOPAN, NPI): Sea 16 moorings; Satellite-based 1997-present Environmental Information Ocean Barents surface Ocean winds Sea Opening (IMR): Cloud information (Norway Bear Island) 1997-present Ozone levels and carbon dioxide 5 current meter moorings Barents Water vapor + Hydrographic observations along the Vegetation Sea section(~6/year) Ocean surface topography Sea Surface Temperature Sea Surface Winds Sea Surface Salinity Sea Ice (concentration and thickness) Ocean color Limitations for remote sensing in the Arctic Ocean: Presence of sea ice Insufficient Svinøy i orbit (UiB) inclination Subsurface 1978-present characteristics (including freshwater content) 2 moorings cannot be directly assessed from the remotesensing ADCP data T/S