Kevin Friedland: Expected Changes in Ocean Dynamics

Kevin begins by acknowledging that his colleague Mike Fogarty was originally supposed to attend. A link to some of their work is here.

What ocean changes do we expect to see in an increasing climate?

• Increased water temperature
• increased melting ice
• changes in salinity due to runoff and evaporation/precipitation patterns
• changes in major current systems
• increased stratification of ocean column
• changes in position and intensity of frontal zones
• changes in upwelling.

He shows us a complex chart of the interactions between these things. Upshot: this is tough to model.

The North Atlantic Oscillation (NAO) is a varying state: a positive phase or a negative phase. Lots of pressure lines in the positive phase; not so many in the negative phase. When there's lots of pressure, there's lots of wind. We're going to see temperature patterns and wind pattern changes; these will impact our precipitation.

The NAO affects recruitment and therefore fishery yields of cod. Cod stocks show a relationship to the NAO that is regional and localized -- large scale forcing factors affect stocks in measurable ways. Kevin shows us a "hideous graph" of plankton and cod recruitment (actually all gadoids -- cod is a gadoid). In one set of years, plankton acted one way; in another set of years, plankton acted another way in the Northeast Atlantic (near Europe). Gadoid productivity corresponded to the plankton health. It appears that the NAO is also connected to lobster productivity in the Gulf of Maine.

Kevin then shows us a series of sea surface temperature measurements from the 1880s to present day in a variety of regions in the North Atlantic. We see the intense warming in the 1950s that Lew showed us across all regions; current temperature is not the highest it's ever been. But over recent decades we are experiencing a greater range in temperatures than we have ever seen: there's a major increase in the difference between summer and winter temperatures that is seen in recent years that has never been true in the rest of the existing record.

Over the past, when things got warm, both summer and winter got warm together. Today, as things get warm, summers are getting MUCH warmer and winters aren't. This is the difference.

Kevin asks us to consider: are we waiting for climate change to occur here in the Gulf of Maine, or has it occurred and we've missed it? Spring warming rates have dramatically increased, and he notes some other metrics (that I missed -- please help fill in) suggesting we may already have seen major changes. These changes will impact biological populations that cannot tolerate high temperatures: look for distribution and range changes to be appearing. Will there be cod in the Gulf of Maine anymore? Will spanish mackerel become the top species?

We see a chart of the distribution of hake across the North Atlantic. The hake are moving north! This is early empirical evidence that populations are moving in response to climate change. Kevin tells us the story of the eel: they seem to correspond to the NAO, but the eel are on their way out. He suggests that this is related to the health of the Sargasso Sea (the "ocean desert" in the tropics), where the eels go to spawn (eel larvae are dramatically interesting fish -- check them out). There's been a diminishment of winds in the Sargasso Sea, which may impact the transport mechanism of the eel larvae. We look at haddock recruitment data connected to the NAO. The upshot: it's hard to predict changes in fisheries when we don't fully understand the mechanism of feeding, lifecycle, and mobility of specific species.

The message: economic species (like eel in the North Atlantic) are impacted by the health of ecosystems very far away.

Conclusions: decadal scale variation in the ocean climate are visible. The NAO is a dominant feature in the region, and impacts cod recruitment and fish distribution. Migratory species may be impacted by factors in distant locations. We expect complex interactions between exploitation and harvesting.



Kevin and Mike's slides are also available online.

Q: for Kevin and Andy: tell us about the salinity anomaly and the NAO (and right whales? didn't catch).
A: Andy: the salinity signal may be masking the NAO variability in calanus. If you remove the herring signal from calanus, the NAO pattern pops right out. Kevin: the systems are much too complex to bring everything down to one or two patterns -- you can't always look at the NAO to explain everything.

Q: as the ice sheet melts in the North Atlantic, what happens to sea surface temperature (warmer, or colder?).
A: Kevin: warmer, I hope. The increase in temperature seems to be a continental effect (and we're seeing an increase in storms that seems to correspond). Melting icewater from Arctic ice sheets is a geographic feature that's unique to us -- might mean that the sea surface temperature INCREASES that are happening globally and here, connecting with land surface temperatures, will be tempered by this influx of cold, fresher water. But it is extremely complex and hard to predict.
A: Lew Incze: these models are so geographically variable, and global modeling is so crude, it's extremely hard to predict. The difference in buoyancy from salinity differences (and, slightly, from temperature differences) are a more major impact on population biology that just the temperature difference alone. The buoyancy changes the way water mixes and the absence of convexity mixing changes the temperature measurements (maybe explains the divergence we're seeing in summer and winter surface temperature -- less mixing in the water column to make summer water colder and winter water warmer).

Q: Calanus question about mixing -- asked by Dan Holland?
A: Andy Pershing: Calanus relies on strong winter mixing to set up the productivity in the spring season. In the late 1990s, we had the best of both worlds: enough mixing to keep them productive, but this burst of freshness that kept the less dense water and the phytoplankton

A: Lew Incze -- we may see a shift in food production of primary producers to smaller, and more mobile species.

Q: Patten White asks -- what is the correlation between cod and temperature -- is that data based on population measurements or commercial landings? (A: landings) Landings data can be heavily impacted by regulatory climate and economics on shore. On the west coast, they are showing the opposite pattern that we are (temperature dropping, increase in large fin fish? please chime in -- I missed just how the patterns differ).
A: Kevin -- really depends which populations on the west coast you are measuring: major differences between species.

Q: NAO positive and negatives related to cod production, regionally around North Atlantic. Are cod moving to chase prey that are moving?
A: Lew Incze -- we don't have the data. We just don't know.

Q: Any impact of wind patterns on fish populations?
A: We think we're seeing that in haddock populations -- we hypothesize the wind has a connection to egg/larval distribution. We're starting to look at this but can't predict yet.
A: Lew Incze: Gulf of Maine isn't predicted to get a lot of wind increase change. Just intensity of storms, not average windspeed.