Observed and projected Changes to the Pacific Ocean

Observed and projected Changes to the Pacific Ocean A. Ganachaud 1, A. Sen Gupta 2, J. Orr, S. Wijffels, K. Ridgway, M. Hemer, C. Maes, C. Steinberg, A. Tribollet, B. Qiu, J. Kruger 1 Oceanographer, Institut de Recherche pour le Développement, Nouméa, New Caledonia 2 SPC, March 3, 2011 Climate modeling expert, Centre for Climate Change Research, University of New South Wales, Sydney, Australia 1

Outline State of the Ocean • Provinces • Currents • Nutrients and oxygen • Vertical structure • Physical processes SPC, March 3, 2011 Projected changes • Currents • Warming and stratification • Waves & Sea level rise 2

Ocean state: Trade Winds and Warm Pool Classical view : The Trade Winds pile up warm waters in the west SPC, March 3, 2011 3

Ocean state: Oceanic provinces SPC, March 3, 2011 4

Ocean state: currents North Equatorial Current • Winds create two broad westward flows in the tropical Pacific South Equatorial Current SPC, March 3, 2011 5

Ocean state: currents • Winds create two broad westward flows in the tropical Pacific • ITCZ and SPCZ influence on the wind field give rise to two eastward counter currents SPC, March 3, 2011 6

Ocean state: currents SPC, March 3, 2011 • Winds create two broad westward flows in the tropical Pacific • ITCZ and SPCZ influence on the wind field give rise to two eastward counter currents • Archipelagoes and coasts lead to strong north-south coastal currents 7

Ocean state: currents • Ocean currents transport nutrients, oxygen and fish larvae SPC, March 3, 2011 8

Ocean state: Temperature Vertical Structure Temperature across the Equator 0 m 100 m 500 m SPC, March 3, 2011 9

Ocean state: Temperature Vertical Structure 0 m Presence of stratification in thermocline 250 m 500 m 0 m 100 m 0°C 10°C 20°C Temperatures 30°C 500 m SPC, March 3, 2011 10

DEPTH Ocean state: Nutrients Dissolved nitrate at 100 m Nutrients are mostly depleted in the euphotic zone Replenishment by remineralization of marine snow SPC, March 3, 2011 Oceanic upwelling or mixing is needed to transfer them to the surface layer Similar features for phosphate & silicate 11

DEPTH Ocean state: Oxygen Dissolved Oxygen at 400 m Oxygen is abundant near the surface and depleted near 400 m Replenishment by high latitude atmospheric input and subsurface transport by ocean currents SPC, March 3, 2011 12

Ocean state: how to supply the euphotic zone ? ? ? SPC, March 3, 2011 1. Upwelling (vertical current; east equator and some islands) 2. Eddies 3. Mixed layer 4. Internal tides. . . against stratification 13

Ocean state: Eddies Small-scale circulation generated spontaneously or by interaction between the large-scale flow and land SPC, March 3, 2011 14

Ocean state: Eddies Small-scale circulation generated spontaneously or by interaction between the large-scale flow and land SPC, March 3, 2011 15

Ocean state: Eddies and land effects Small-scales generated spontaneously or by interaction between the large-scale flow and land Boundary currents SPC, March 3, 2011 16

Ocean state: Eddies and land effects Small-scales generated spontaneously or by interaction between the large-scale flow and land Boundary currents Upwelling SPC, March 3, 2011 17

Ocean state: Eddies and land effects Small-scales generated spontaneously or by interaction between the large-scale flow and land Boundary currents Upwelling Vertical mixing for internal tides SPC, March 3, 2011 18

Ocean state: Mixed layer Seasonal variations of the mixed layer depth pumps deep nutrients towards the sunlit zone SPC, March 3, 2011 19

Variability Global Warming PDO El Nino Seasonal Eddies Internal tides SPC, March 3, 2011 Courtesy J. Lefèvre, IRD 20

Global Warming What changes were detected over the past ~50 years ? What do IPCC projections suggest ? SPC, March 3, 2011 21

Global Warming: Ocean Models Temperature (27°C) Salinity (34 ppt) Current Laws of Physics Courtesy A. S. Gupta Grid Size SPC, March 3, 2011 22

Global Warming: Ocean Models SPC, March 3, 2011 23

Global Warming: Ocean Models How an Ocean model sees the ocean … SPC, March 3, 2011 Grid Size 24

Global Warming: Ocean Models How an Ocean model sees the ocean … Grid Size The grid box only contains information for the average current Courtesy A. S. Gupta SPC, March 3, 2011 25

Global Warming: Ocean Models How an Ocean model sees the ocean … Grid Size The grid box only contains information for the average temperature Courtesy A. S. Gupta SPC, March 3, 2011 26

Global Warming: Ocean Models How an Ocean model sees the ocean … Coarse resolution o. Broad features are captured But: o. Cannot see small islands o. Cannot see fine scale circulation o. These features may be important for island processes. . . and large scale features Courtesy A. S. Gupta SPC, March 3, 2011 27

Global Warming: Ocean Models How an Ocean model sees the ocean … Grid box size in the different models range from about 1° to 5° Courtesy A. S. Gupta SPC, March 3, 2011 28

Ocean Models: are they any good ? Observations (Had. ISST) Surface Temperature All the models are able to capture the main features of the Pacific Ocean: Average of 19 models Courtesy A. S. Gupta SPC, March 3, 2011 29

Ocean Models: are they any good ? Observations (Had. ISST) Surface Temperature All the models are able to capture the main features of the Pacific Ocean: o. Warm Pool Average of 19 models Courtesy A. S. Gupta SPC, March 3, 2011 30

Ocean Models: are they any good ? Observations (Had. ISST) Surface Temperature All the models are able to capture the main features of the Pacific Ocean: o. Warm Pool o. Cold Tongue Average of 19 models Courtesy A. S. Gupta SPC, March 3, 2011 31

Ocean Models: are they any good ? Observations (Had. ISST) Surface Temperature All the models are able to capture the main features of the Pacific Ocean: o. Warm Pool o. Cold Tongue o. S. American upwelling Average of 19 models But in most models: o. Warm pool is not warm enough o. Cold tongue extends too far west Courtesy A. S. Gupta SPC, March 3, 2011 32

Projected changes to the circulation Ocean currents • SEC weakens on the equator • EUC moves upward • Eastward SECC weakens • Little change in the subtropical gyres Changes 2100/A 2 versus 2000 Average over 13 IPCC projections SPC, March 3, 2011 33

Temperature: recent changes Warming ~1°C down to 100 -200 m Weaker warming or even cooling below thermocline Enhanced stratification Temperature change over past 50 yr (Durack & Wijffels, 2010) Contours are average temperature SPC, March 3, 2011 34

Temperature: recent changes. . . and projections More warming ~2°C down to 80 m Weaker warming or cooling below thermocline Even more stratification Multi-model projected temperature change (13 IPCC models; A 2/2100 versus 1980 -2000) SPC, March 3, 2011 35

Nutrient supply recent changes Observed changes in nutrient concentrations o Over the past 20 years: Only two time series o One suggests a decrease, the second one no trend o Too few data to be conclusive ! Phosphate concentration in the mixed layer (Watanabe et al. 2005) SPC, March 3, 2011 36

Nutrient supply recent changes. . . and projections What controls nutrient concentration: o Biological activity o Supply to the euphotic (sunlit) zone from deep ocean: o Stratification o Ocean currents o Turbulence in the mixed layer o Upwelling o Eddies SPC, March 3, 2011 Phosphate concentration in the mixed layer (Watanabe et al. 2005) 37

Nutrient supply recent changes. . . and projections Projections (2100/A 2): o Stratification increases by 20 -30%; especially in the Warm Pool SPC, March 3, 2011 38

Nutrient supply recent changes. . . and projections Projections (2100/A 2): o Stratification increases by 20 -30%; especially in the Warm Pool o The winter mixed layer shallows by ~20 m; o Equatorial upwelling decreases, but region-wide 9°S-9°N upwelling remains constant. SPC, March 3, 2011 39

Nutrient supply recent changes. . . and projections Projections (2100/A 2): o Stratification increases by 20 -30%; especially in the Warm Pool o The winter mixed layer shallows by ~20 m; o Equatorial upwelling decreases, but region-wide 9°S-9°N upwelling remains constant. SPC, March 3, 2011 All factors suggest reduced nutrient supply and therefore biological activity 40

Dissolved oxygen recent changes Stramma et al. 2008 o More oxygen data than nutrient o Major decrease of dissolved oxygen in the remineralization zone with westward extension of the oxygen minimum zone (OMZ) SPC, March 3, 2011 41

Dissolved oxygen recent changes. . . and projections Stramma et al. 2008 Dissolved oxygen concentration is expected to continue to decline due to high latitude ocean warming Low oxygen areas are expected to expand SPC, March 3, 2011 42

Acidification: recent changes Change in surface p. H for last 10 yrs When additional CO 2 dissolves in the ocean, ocean acidity rises. From: Pacific Science Association, 2007 SPC, March 3, 2011 This makes it more difficult for corals and certain phytoplankton species to grow -0. 06 p. H units ([H+]decreased by 30%) 43

Acidification: recent changes. . . and projections Change in surface p. H for last 10 yrs • Another decrease of 0. 2 to 0. 3 p. H units is expected • The aragonite saturation horizon is expected to shallow to 150 m depth From: Pacific Science Association, 2007 SPC, March 3, 2011 44

Two more actors: Waves and Sea Level SPC, March 3, 2011 45

Wave climate Projected increase (or decrease) to significant wave height Wang and Swail, 2006 SPC, March 3, 2011 • Too few observations to determine CC trends • The wave "climate" is related to ENSO and other climate signals • Only few projections; not resolved by IPCC models 46

Sea level rise • As water warms it expands • As ice-sheets and glaciers melt they increase ocean volume +20 cm over 100 yrs Increasing sea level: • Alters oceanic ecosystems/habitat • Changes shape of coastlines • Changes nature and extent of mangrove SPC, March 3, 2011 47

Sea level rise +20 cm SPC, March 3, 2011 • New published estimate suggest IPCC AR-4 was too conservative: +1 m to +2 m possible • Regional deviations are of O(5 cm) 48

Conclusions on the tropical Pacific Ocean • Ocean is warming, with enhanced signal in the upper 100 -200 m • Stratification limits nutrient supply; mixed layer reach is reduced • Some ocean currents have changed and will change; Equatorial divergence region projected to shrink SPC, March 3, 2011 • Dissolved oxygen decreases; ocean becomes more aciditic • Sea level has risen by ~20 cm; could rise by another 1 -2 m 49

SPC, March 3, 2011 50

Extra information SPC, March 3, 2011 51

Nutrient supply recent changes. . . and projections Multi model change in density with depth Warm, ‘light’ water 1990 o Surface water becomes ‘lighter’ more than deep water, due to: § Surface warming § Surface freshening o Increased stratification inhibits mixing 2090 Cold, ‘heavy’ water SPC, March 3, 2011 Courtesy A. S. Gupta 52

Nutrient supply recent changes. . . and projections Multi model change in density with depth Light available Biology Low nutrients 1990 2100 Barrier to mixing o Surface water becomes ‘lighter’ faster than deep water, due to: § Surface warming § Surface freshening o Increased stratification inhibits mixing o Less mixing means less nutrients can be brought to surface No light No biology High nutrients SPC, March 3, 2011 Courtesy A. S. Gupta 53

Ocean Models – are they any good? Observations (Had. ISST) ENSO Most models shows ENSO -like behavior. Average of 18 models SPC, March 3, 2011 But Different degrees of realism (too strong, too weak, too periodic, wrong season) Almost all models have ENSO warm patch too far west 54

Ocean Models – are they any good? Observations (CARS 06) Surface Salinity Averaging across the different models the general observed pattern is captured Average of 13 models SPC, March 3, 2011 55

Pacific Ocean circulation SPC, March 3, 2011 Source: Fieux, M. 2010 56