What is SST?
Sea surface temperature (top metre or so)
What are the figures regarding how warm the oceans are?
For most of the oceans, the warmest decade ever recorded was the most recent, steady warming trend of a tenth of a degree per decade
The 20 years up to 2017 included 18 of the hottest global annual SSTs ever recorded
What makes the water warm up faster than air?
It take up heat 4000 times more effectively than air as it is very dense
What percentage of the heat generated by anthropogenic warming has been absorbed by the oceans?
90%
How high was 2017’s OHC value?
- Equivalent to almost 700x chinas total annual electricity generation
How do El Nino events lead to smaller Ocean Heat Content (OHC)
- El Nino causes warming of surface ocean temps
- Warmer surface waters lead to increased heat transfer from deeper ocean layers to the surface atmosphere (Ocean-atmosphere coupling)
- Warmer surface waters release heat that was previously stored in the deeper ocean layers
What are the three options to respond to warming as a marine organism?
Move, Adapt or Suffer consequences
What is the evidence for organisms that ‘move’ as a response to warming?
- Moving is the first thing fish do
- Studies have counted and tracked every fish and then carried out species level analysis
- Northern affinity fish abundance decreases with warming as they are adapted for cold
Which fish specifically have decreased in abundance?
- Haddock and cod because they like cold
Why don’t all fish move?
- Temp isn’t the only thing that dictates where a fish lives, many are tied to specific habitats
- Oceanographic structure can be important, norther doesn’t always mean cooler
-Shifting deeper isn’t alway possible
What is meant by the leading edge and trailing edge of species range?
Leading edge = advancing boundary of a species’ distribution
Trailing edge = rear or retreating boundary of a species’ distribution
At trailing edge we may expect species to die as it gets too warm
Other populations can expand in to waters that used to be too cold but are now suitable
How do phytoplankton respond to environmental changes?
- rapidly, the timing of phytoplankton blooms has advanced much faster than that of plants on land
- animals that feed on phytoplankton e.g. larval fish have advanced their key advanced even faster than the phytoplankton
What is the only problem with phytoplankton being able to adapt quickly?
- there’s different responses based on trophic levels can lead to temporal mismatches which can lead to affected food webs
What is the problem associated with coral bleaching?
- Bleaching itself isnt lethal but they need time to recover between bleaching events
- This gap is shortening giving less time to recover and less chance of mortality
Give the characteristics of cold water corals
- Create important habitats
- Reefs in scotland -Desmophyllum
- Provide rich feeding grounds and important breeding areas
- Models project decrease of 28% to 100% in suitable habitat
Give characteristics of Kelps
- Foundation species
- V.productive and diverse
- Diff. kelp species around the world respond differently e.g. extinction, range expansion, abundance decrease etc.
- Low latitudes more likely to cause extinction as water just gets too warm
How is pH measured and why is it worth acknowledging?
pH is a measure of H+ concentrations and its a logarithmic scale
So a small change is actually huge
- when you plot pH in terms of H+ ions rather than pH units the increase is much more steep
What is the chemistry of ocean acidification?
- Some of the C02 entering the sea remains as gas but it can also be taken up by marine photoautotrophs through photosynthesis
- remaining C02 combines with water and forms carbonic acid
- When carbonic acid is dissolved in water it dissociates into Hydrogen ions and Bicarbonate ions
- Most hydrogen ions will combine with carbonate ions creating bicarbonate ions which reduces the pool of carbonate ions in sea water
What happens when you decrease carbonate ions?
- Many marine organisms build hard parts out of calcium carbonate
- Various forms of calcium carbonate are used e.g. aragonite, calcite etc.
- Organisms need to extract calcium and bicarbonate ions from seawater to form calcium carbonate (this releases C02 and water in the process)
What is the positive feedback loop with the production of calcium carbonate?
- Producing calcium carbonate emits more c02 in to the water, which creates carbonic acid and further reduces the pool of carbonate ions
How hard is it for organisms to produce these hard structures?
- Seawater chemistry influences how difficult organisms will find it to produce their calcium carbonate hard parts
- Can be quantified with the saturation states of different forms of calcium carbonate
What are the results you would conclude from looking at the saturation state equation?
- > 1 is considered supersaturation so shell building is easy and structures will stay intact
< 1 is considered undersaturation which favours dissolved ions and its difficult to build anything with solid calcium carbonate, easily broken down by seawater
Coral reefs need a saturation state significantly above 1 need at least 3.25
In what ways are we approaching a ‘hot house period’ regarding oceanic pH
Current surface pH is lower than it has been for at least 2 MY so we don’t know what the modern effect on marine life is going to be
What is CCD?
Calcium compensation debt , if you go well below it calcium structures start to dissolve
- There is usually a balance between C02 in sea (acidification) and mineral input from weathering (alkalinity)
