Climate Change: The Ocean’s Response Richard J. Cowlishaw, Ph.D Southwestern College Winfield, KS

Key Threats to Ocean Ecosystems International Programme on the State of the Ocean (IPSO) report highlights key threats to ocean ecosystems Pollution Bycatch Overfishing Eutrophication Aquaculture Habitat Alteration Invasive Species Coastal Development Climate Change http://www.stateoftheocean.org/science/state-of-the-ocean-report/

The Big Heat Sponge Oceans have absorbed 90% of the heat generated by humans Heat capacity of the ocean has limits Atmospheric warming will accelerate when limit is reached Nuccitelli et al. 2012

Deep Ocean Heating Heat penetrates to ocean depths over time Glecker et al., 2016 Nature Climate Change Large volcanic eruptions in the past (black triangles) have a cooling effect on the atmospheric and ocean temperature. Small simulated eruptions have little effect. Half of the forced heating of the ocean has occurred since 1997, reflecting the recent acceleration of the planet’s warming. Heat penetrates to ocean depths over time

Warming Impacts on the Ocean Alteration of surface currents Weakening of thermohaline currents Strengthening of permanent thermocline Sea-level rise

Ocean Circulation Surface winds drive movement of water Surface currents distribute heat between equator and poles Spherical shape of planet and its rotation causes currents to deflect along their path Right deflection in Northern Hemisphere Left deflection in Southern Hemisphere Establishes ocean gyres

Ocean Surface Circulation Warm air/water to north, cold air/water to south

Europe: So North Yet So Temperate Gulf Stream – conveyor of heat to high latitudes

Deep Ocean Currents Super-cooling at the poles Cooling and ice formation  increased density Cold, oxygen-rich water sinks to depth Forms deep bottom water currents Thermohaline currents

Overturning of the ocean volume on a 1000-year scale

Reducing Ocean Circulation Decreasing temperature differences between poles and equator – weakens or alters surface currents Potential cool down Europe – weakening of Gulf Stream Freshwater from melting ice reduces seawater density  reduces bottom water formation Reduce the amount of oxygenated water at depth – threat of hypoxia in deep ocean

Strengthening Thermocline Thermocline – depth interval of rapid temperature change Density gradient Separates surface waters from the deeper ocean Warming air temperatures will likely strengthen it Reduce primary production and CO2 uptake by ocean (Cold) Dissolved Nutrients (Warm) Light http://marinebio.org/oceans/temperature/

Sea-Level Rise Average sea level rising 1.5-2.0 mm annually 21st century projections: 180-590 mm (7.0-23 inches) Ways sea-level can rise with global warming Melting of land ice sheets and glaciers Thermal expansion – warm water occupies greater volume than cold water Uncertainties on how much and when >600 million people at risk by rising seas

IPCC 2014 Sea Level Rise Projections Past and future sea-level rise. For the past, proxy data are shown in light purple and tide gauge data in blue. For the future, the IPCC projections for very high emissions (red) and very low emissions (blue,) are shown. Source: IPCC AR5 Fig. 13.27.

Correlation of CO2 and Sea-level Figure is somewhat dated. CO2 concentrations have recently crossed the 400 ppm mark, ahead of the 2020 projection. We can infer that temperature levels rose and fell with CO2 levels across this time line. Rise and fall of CO2 reflect the sequence of interglacial and glacial periods respectively

Ocean Acidification CO2 uptake by oceans has two consequences: Offset human-produced CO2 emissions Increase the acidity of the oceans Ocean pH has decreased by 0.1 pH units since 1860  30% increase in acidity

Predicted Impacts on Marine Life Increasing water temperatures Changes in timing and location of primary production – decrease in food predictability Change in ranges and migration patterns Mobile species - Relocation to cooler waters Sessile species – tolerate, evolve or die Coral bleaching and die-back Increased threat of water-borne diseases Increasing hypoxia in deeper waters

Predicted Impacts on Marine Life Increasing acidity Reductions in calcifying organisms, those with calcium carbonate structures (i.e. shells) Span the food chain: algae, protozoa, zooplankton, corals, echinoderms, crustaceans, molluscs Blood acidosis; reduced metabolic rates Suppressed immune systems Impaired olfaction and feeding behavior Noisier ocean – problems of sound-dependent species

The Sixth Great Extinction Event Permian Extinction (The Great Dying) 252 million years ago 96% of all marine species and 70% of all terrestrial species went extinct Causes? Not clear, but climate change and change in ocean circulation was certainly in the mix Evidence that the next great extinction event is underway Major difference: Brought upon by another species (humans)

An Ocean in Crisis We’ve arrived at the tipping point for the oceans Oceans are big but have limits – we are realizing those limits One billion people unsustainably rely on the oceans for their protein – what will 2050 look like? Without action on climate change we will push the Sixth Mass Extinction forward