Seabird Die-off Near Kodiak Island, 2015

Ten years ago this month, my wife and I took a fishing charter off the south coast of Kodiak Island.  We launched into the ocean from a gravel beach near our lodge.  As soon as we were in open water, we noticed a dead sea-bird floating on the water.  Then another.  Then another.  There were dead birds on the water, spaced about every 50 to 100 yards (meters).  As we sailed, we saw more dead birds.  We traveled about 20 or 30 miles from shore that day, going into deeper waters to fish for halibut.  We saw dead birds the whole day – dead birds all the way to the horizon.

The birds were murres and kittiwakes.  Murres look a bit like penguins, and kittiwakes look like seagulls.  The die-off near Kodiak was part of a much bigger die-off of seabirds along the entire south Alaska coast.  Biologists’ autopsies showed that the birds starved to death.  Reports say that 4 million murres died, about half of the total population.  It was one of the largest single-species die-offs on record.  The biologists’ maps that I saw didn’t even include the birds that died near Kodiak. 

The waters near Alaska are normally some of the most productive in the world.  Deep waters normally rise to the surface in a process called “upwelling”, carrying nutrients from the ocean floor.  Those nutrients sustain a robustly abundant marine food chain from plankton to humpback whales.  Arctic waters are prolific because the water is the same temperature, and therefore density, from the sea floor to the surface.  Nutrient-rich deep waters easily rise to the surface because temperatures are constant from the surface to the sea floor.

In 2015, the northern Pacific experienced an abnormal, persistent area of warm water, termed a marine heat wave, or less technically, “The Blob”.  The warm water stratified the water column, with warm water floating on top of the denser cold water below and blocking the upwelling currents.  Deep waters no longer flowed to the surface.  Nutrients didn’t reach shallow water, and millions of birds starved to death.  Other species were noticeably impacted.  Chinook salmon abundance declined.  The following winter, the number of humpback whales migrating to Hawaii fell by 50%.  After ten years the population of murres has still not recovered.  

This morning, I saw a report that “The Blob” had returned to the North Pacific, which prompted me to write this post.

Oceans are warming world-wide, from the surface downwards.  Warmer surface waters increase the chances of a marine heatwave. 

We understand what is happening, why it is happening, and we can expect more damage to the North Pacific birds, fisheries and whales as warming continues.

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Common Murre image credit: Dick Daniels (http://carolinabirds.org/), Wikimedia Commons
Kittiwake image credit:  Yathin S Krishnappa – Wikimedia Commons.  (https://commons.wikimedia.org/w/index.php?curid=24551364)

Global Heat Budget #2: Oceans

The world’s oceans are warming.  Ocean warming is the strongest confirmation that greenhouse gases are warming the planet. 

The heat capacity of water is among the highest of common substances.  That means that water can absorb a large amount of heat while its temperature changes only slightly.  The measurable warming of the world’s oceans indicates that a very large amount of heat has come from somewhere.  The only credible source for so much heat is the retention of heat by atmospheric greenhouse gases.  Let’s look at the source of the data, and the numbers.

ARGO Oceanographic Program

Rising ocean temperatures have been measured by oceanographic surveys since the 1970s.  However, these ocean surveys were limited in geographic coverage and continuity of data acquisition.  A more comprehensive system, ARGO, was put in place beginning in the early 2000s, with improvements and new deployments continuing today.  Today, ARGO consists of nearly 4000 floats which continuously measure ocean temperature, salinity, density and currents from the surface to 2000 meters. 

ARGO floats measure temperature to an accuracy of two-thousands (0.002) of a degree Celsius.  The floats are “parked” at 1000 meters, and every ten days submerge to 2000 meters and return to the surface, where data is broadcast to satellite receivers.  The system provides comprehensive coverage worldwide except for polar latitudes, and continuous measurements.

Ocean *Weather*

Like the atmosphere, ocean temperatures are seasonal, cyclic, variable, and turbulent.  The large number of ARGO floats was designed to adequately measure and characterize the variable temperatures of the ocean.  The volume of data acquired allow scientists to make maps of the changing water temperature and calculate the total heat content in the ocean.

Observations

Surface temperatures are warming the fastest.  NOAA presents charts of average ocean temperature and ocean heat content according to water depth, based on ARGO observations and earlier oceanographic studies.

Surface waters (0 – 100 m) have warmed by about 0.6 degrees C on average since the late 1960s. 

Intermediate waters (0 – 700 m) have warmed by a little over 0.2 degrees C on average since the late 1960s. 

Relatively deep waters (0 – 2000 m) have warmed by about 0.1 degree C on average, since the late 1960s.

Over all depth increments observed, the rate of warming seems to be slightly increasing.

Heat Content

The changing heat content of the ocean is a simple function of the change in temperature.  The heat capacity (or specific heat) of water represents the amount of heat required to change the temperature of a given volume of water.  From an observed change in temperature, we can back-calculate the amount of heat that has entered the ocean.  The density and heat capacity of water change slightly with pressure (and water depth).  NOAA has calculated the heat content of the ocean over various depth intervals from the temperature data and heat capacity.  

The heat content of the ocean at intermediate depths (0 – 700 m) has increased by about 2 x 10²³ joules since the late 1960s. 

The heat content from the surface to 2000 meters (0 – 2000 m) has increased by about 3 x 10²³ joules since the late 1960s.  This means that the heat content over the interval from 700 m to 2000 m has increased by about 1 x 10²³ joules, about half of the increase in heat content at intermediate water depths.

Source of Increasing Heat

NOAA unfortunately did not report temperature change or heat content in separate depth intervals, but only in overlapping intervals of 0 – 100 , 0 – 700, and 0 – 2000 meters.  Starting from the average change of temperature for each interval, I calculated the heat content for 0 – 100 m, 100 – 700 m, and 700 – 2000 m.  My figure for total heat content calculated from temperature change exceeds the heat content reported by NOAA by 14%, probably due to errors in my single-point values for temperature or heat capacity over these depth intervals.

	Temp Rise (C)	Volume (km3)	Density (g/cc)	Mass (kg)			Heat Capacity (J/kg-C)	Change in Heat Content (J)
0 - 100 m	0.6	5.23E+07	1.025	5.10E+19			3928.00	1.20E+23
0 - 700 m	0.2	3.69E+08	1.034	3.57E+20			3421.50	2.44E+23
0 - 2000 m	0.1	1.36E+09	1.329	1.02E+21			3339.04	3.41E+23

Intervals	Change in Heat Content	Percent of Heat Change	Change in Heat Content per 100 m
0 - 100 m	1.2E+23	35%	1.2E+23
100 m - 700 m	1.2E+23	36%	2.1E+22
700 m - 2000 m	9.6E+22	28%	7.4E+21

There is a large difference between the heat gained in the upper 100 meters of the ocean and the heat gained at deeper levels by equivalent volume.  The ocean is clearly heating from the surface downward.  About 35% of the total heat increase has occurred in the upper 100 meters of the ocean, about 36% in the next 600 meters, and about 28% in the next 1300 meters.  Research on deep ocean currents shows that heat is also being introduced into the deep ocean by currents, rather than by conduction. 

The geographic distribution of ocean heating also shows atmospheric influence.  The ARGO ocean data shows distinct heating anomalies between 30 and 40 degrees of latitude, north and south.  These are the down-welling points of large atmospheric convection cells termed Hadley cells.  You can see atmospheric circulation in observations of ocean warming.

Conclusion

The first post in this series quantified anthropogenic heating and cooling, primarily from greenhouse gases, particularly CO2.  This post looked at the largest heat sink on earth – the oceans.  

Net Anthropogenic heat absorbed by the planet from 1970 to 2016 was about 3.4 x 10²³ joules.  Over the same period, the heat content of the oceans has increased by about 3.0 x 10²³ joules.  Anthropogenic heat is the only credible source for the heat appearing in the ocean, and the warming oceans confirm that greenhouse gases are, in fact, warming the planet.  

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References

Global Heat Budget #1: Anthropogenic Heat

 http://dougrobbins.blogspot.com/2018/04/global-heat-budget-1-anthropogenic-heat.html] 

https://www.nodc.noaa.gov/OC5/3M_HEAT_CONTENT/index.html

Ocean heat content figures.

https://www.nodc.noaa.gov/OC5/3M_HEAT_CONTENT/index3.html

Ocean temperature figures.

https://www.nodc.noaa.gov/cgi-bin/OC5/3M_HEAT/showfiganom.pl?action=start

Gridded temperature data in map view.

The Oceans Their Physics, Chemistry, and General Biology, UC Press E-Books Collection, 1982-2004, University of California Press 

https://publishing.cdlib.org/ucpressebooks/view?docId=kt167nb66r&chunk.id=d3_4_ch03&toc.id=ch03&brand=eschol%20

Physical properties of sea water.