Climate Change Impacts the Deep Sea

The deep sea faces multiple threats including

over-extraction (living and non-living), pollution, and climate change

These anthropogenic impacts on the deep sea are likely to be _, and should be considered together

synergistic

How do synergistic impacts affect an organism's capacity?

Multiple threats tax organisms so heavily that they exhaust their capacity for adaptation, making the overall impact much worse than individual threats added together

Why is it important to consider deep-sea impacts together rather than individually?

Because they are synergistic; looking at one threat in isolation underestimates the true damage to the community.

Larval transport is likely to be impacted by both

mineral extraction and climate change → the way larva move from one place to another will be impacted by physical activities of mining and by the chemical and temperature changes associated with climate change

If you identify key habitats and you prevent fishing or other activities in certain marine protected areas, then it can lead to

more fish being available and increased fisheries yield outside of that MPA

There is a lot of carbon in the atmosphere, and a lot of it is dissolved in

the ocean

There is lots of organic carbon in bodies of organisms in

the ocean and on land. And the fluxes being the movement between those different reservoirs.

What are the three primary reservoirs of carbon mentioned?

1. The atmosphere

2. Dissolved in the ocean

3. Organic carbon in the bodies of organisms (land and sea).

In the context of the carbon cycle, what is a Flux?

The movement of carbon between different reservoirs.

Human emissions, in particular burning fossil fuels is moving a lot of inorganic carbon, mostly

carbon dioxide, moving that carbon from long term storage below the ground in coal, oil, natural gas, putting it in the atmosphere.

And the ocean is doing a lot of work to take up

some of that excess carbon → buffering to some extent the anthropogenic greenhouse gas emissions

Both the deep ocean and buried ocean sediments are the massive

reservoir of carbon (huge amount of carbon)

Carbon dioxide diffuses into the ocean carbon cycle through the

air-sea surface exchange

More carbon is moving into the ocean in

warmer parts of the ocean

Once carbon dissolves into the seawater, that carbon dioxide can enter the ocean carbon cycle through what three different mechanisms?

The physical C pump (physical)

The biological C pump (biological)

The carbonate pump (chemical)

Where does the initial diffusion of CO₂ take place in the physical pump?

At the air-surface interface (where the atmosphere meets the water).

What two types of physical ocean movements drive the carbon pump?

Surface currents and deep ocean currents.

What are the two vertical processes that drive the movement of carbon in the water column? (physical carbon pump)

Downwelling (moving carbon down) and upwelling (moving carbon up).

How does the physical pump move carbon throughout the ocean?

throughout the ocean?Through the diffusion of CO₂ at the surface and the physical circulation of water masses (currents).

Deep water formation

In the Atlantic where surface water sinks and becomes deep water

What is the common name for the large-scale system of ocean currents that moves carbon globally?

Global Ocean Conveyor Belt (simplified)

Biological Carbon Pump

Phytoplankton doing photosynthesis in the surface water, taking that inorganic carbon → converting it into organic carbon → once consumed by other organisms, that is part of the biological carbon pump. Relates to Dial vertical migration and sinking of marine snow (organisms moving carbon from surface water to deep water)

What system is very important to marine organisms such as coral, oysters, calms, and lobsters building their shells (organisms that build a calcium carbonate shell)

The ocean carbonate system

The ocean carbonate system connection to Biological pump

Sinking shells bring carbon down to the deep ocean (deep sea sediments)

The chemical processes that happen that can sort of overall be described as ocean acidification

When carbon dioxide diffuses into water it becomes carbonic acid → more CO₂ the more carbonic acid that dissociates into hydrogen ions and bicarbonate ions

More carbon dioxide in the ocean leads to

increasing acidity (ocean acidification)

Any organisms that builds a calcium carbonate shell has a harder time doing that

in more acidic conditions (calcium carbonate in a strong enough acid will dissolve)

What are the four primary deep-sea impacts caused by increased atmospheric GHGs (carbon dioxide, methane, etc)?

1. Increasing temperature

2. Decreasing oxygenation (the warmer a liquid is, the lower [ ] of dissolved gasses it can hold)

3. Increasing acidity (lower pH)

4. Decreasing food/nutrients (POC, Particulate Organic Carbon)

How does the food supply for deep-sea organisms change due to climate change?

There is decreasing food/nutrients (a reduction in the "marine snow" or POC falling from the surface).

What percentage of anthropogenic $CO_2$ emissions have been absorbed by the oceans?

~30% (carbon dioxide absorbed) → thermal buffering

How much of that absorbed CO₂ is found below 400m?

1/2

How much of the total anthropogenic CO₂ is found below 1000m?

1/5

What percentage of the heat trapped by GHGs has been absorbed by the oceans?

90%

How much of the trapped heat is stored below 700m?

~1/2 (specifically 42% of total heat).

What is the primary biological consequence of ocean warming mentioned?

Warming influences primary productivity

What percentage of Earth's total accumulated energy is stored in the Oceans?

93%

Sea Surface Temperature Anomaly

is basically comparing sea surface temperatures to baseline pre anthropogenic climate change → positive values, part of ocean surface is warmer than expected, blue values cooler. Not seeing red everywhere, but especially in the Artic there are very warmer areas there

What are the three main benefits of using Global Climate Models?

1. They work at a Global scale.

2. They become more precise with more/better data.

3. They allow comparisons.

What are the three main limits of using Global Climate Models?

• Limited data → only as good as the data we have

• Don’t include all surface-depth linkages (not a lot of models integrate benthic and pelagic habitats)

• Scale (generally larger than many seafloor features) → breaking earth up into grids, usually units are larger than many seafloor features, cant factor a specific hydrothermal vent or something

Modeled environmental changes at the deep seafloor in the year 2100

• Arctic and some of the coastal areas predicted to have the greatest increases in temperature

• Dissolved oxygen →

• Seafloor POC flux → less carbon down to the seafloor

• pH - blue areas predicted to be more acidic

Climate change will affect polar regions in terms of POC flux how?

An increase in polar regions for POC flux

Predicted effects of climate change on deep-sea benthic ecosystems in terms of metabolism

In general for most organisms when you increase temperature, metabolic rates will increase

When metabolic rates increase that means organisms are using up more

oxygen in benthic ecosystems in terms of climate change

As temperature increases, they predict that body size will

decrease (higher metabolic rates, limited food) in benthic ecosystems in terms of climate change

Predicted effects of climate change in benthic ecosystems in terms of oxygen concentration

• Macro and megafauna, would decrease as oxygen concentrations decrease

• Benthic biomass/sediment mixed layer depth will decrease

• Habitat will be compressed

• Shift from larger to smaller organisms

Predicted effects of climate change in benthic ecosystems in terms of pH

• Abundance and diversity of calcifiers will decrease (increase of acidity)

• Metabolism/energy demand/shell dissolution → more energy into making and maintaining shells

Predicted effects of climate change in benthic ecosystems in terms of POC flux

• Biodiversity up and down

• Sediment mixed layer depth will decrease, driven by oxygen and by amount of carbon

• Microbial contribution to C-cycling increasing

• Biological pump increase in the contributions of microbes as bigger organisms will decrease

What about climate change predictions for the pelagic? Very hard to model

Benthic predictions might be easier to model. 3D habitat (vertical and horizontal contributions) → huge biogeographic ecoregions that are hard to model

Very poorly characterized

Huge mesopelagic fish biomass

Mesopelagic food webs provision deep-sea species

Biogeochemical cycling

What are the two types of stress responses that need more study for deep-sea species?

Chronic (habitat increased over y years, hard to picture) vs accute stress (lab setting stress, what we mainly do)

Besides steady trends, what kind of events require more research to understand threats?

Intermittent events → frequency of these events

The Ocean Decade Action seven decade outcomes

• Clean Ocean

• Healthy and resilient ocean

• a predicted ocean

• A safe ocean

• A sustainable harvested and productive ocean

• A transparent ocean

• An inspiring and engaging ocean

UN report (2022), actions that can be taken to help climate change

• National governments international cooperation → we can consider on who we decide to vote for and advocate

• Subnational government → smaller scale changes

• Businesses → who we support

• Citizens → consume sustainability, use public transportation, etc.