L22 Flashcards
Sea surface temperature (SST)
- Does Not vary lots in shallow waters
- Measured easily
Global ocean temperature anomalies
-Started fluctuating increasing in mid 20th century
- From late 20th century pretty much increasing year on year
-Most oceans dominated by warmest temperature in the most recent decades
How much of Earth’s water occurs in the oceans?
97%
Mean ocean depth is…?
Nearly 4km
More than …% of the heat generated by anthropogenic global warming since 1971 has been absorbed by our seas
93%
Ocean heat content
- Dominated by most recent years values
- Huge energy values
- some fluctuation, relatively cooler OHC in 2016 was due to large el nino output of heat from deeper oceans
The increase in ocean heat in 2017 was equivalent to almost ? times China’s total annual electricity generation
700
Greenland melt extent 2021
- Consequence of the large amount of heat energy put into the ocean
Possible ecological responses to warming
Move, adapt or suffer consequences
Shifting fish: a case study
- European continental shelf fish form the basis of hugely significant commercial fisheries
-Important for components of marine food webs eg as food for sea birds and mammals - Therefore they are well monitored
Shifting fish: a case study, Fish data
-Data from 25,612 bottom trawl sample hauls between 1980-2008
-Comprised of >100 million fish from 177 species
- Northern and southern affinity fish
- More northern species are declining eg atlantic cod
- More southern species are increasing eg red mullet
Conclusions
-This study found that the presence or absence of speciesin grid squares remained rather constant over decades
-But significant temperature-driven responses in local
species abundance in 39 of the 50 most common species
-There were also changes in assemblage composition associated with warming in 93% of the North Sea cells
- Some fish species certainly are moving in response to climate change
- Others are responding in abundance without necessarily changing their spatial distributions
How has responses to climate change influenced commercial fisheries:
landings of the nine species identified as declining in warm conditions (e.g. haddock, cod) fell by a half
landings of the 27 species identified as increasing in warm conditions (e.g. hake, dab) increased 2.5 times
Why dont all fish move? Temperature is not everything
- When it gets too warm, marine species can move polewards or deeper to find cooler water
Many fish species are tied to specific key habitats, at least for part of their lives
Oceanographic structure can also be important - e.g. in the North Sea, North ≠ cooler (at least not always)
Equally, shifting deeper is not always possible
North Sea fish response - shifting deeper
But the capacity of fish to remain in cooler water by changing their depth distribution had been largely exhausted in the 1980s
Fish with preferences for cooler water are being increasingly exposed to higher temperatures
