North Pacific Marine Science Organization

PICES Press Vol. 22, No. 2

Unusual warming in the Gulf of Alaska
by Howard Freeland and Frank Whitney
In March 2014 there was something very unusual occurringin the Northeast (NE) Pacific that might have substantial
consequences for biota in the Gulf of Alaska andsouthward into the subtropics. A quick examination of theReynolds sea surface temperature (SST) data set shows
considerably higher than normal temperatures in early 2014.
Each month since November 1981, these data have been
published by NOAA/NCEP (ftp://ftp.emc.ncep.noaa.gov/c
mb/sst/oimonth_v2/) and represent the best estimate of theSST in the global oceans (see also Reynolds et al., 2007).
A January mean state, including a field of standard
deviations, for the N.E. Pacific was computed by averaging
the SST fields for all Januaries from 1982 to 2013 inclusive.
An anomaly field was then computed for January 2014 by
subtracting the mean state and normalising by the field ofstandard deviations. Similar calculations were done for
February 2014.

at a pressure of 4 decibars to avoid pumping surface films
into the conductivity cell. In Figure 1b Argo data wereinterpolated to Ocean Station Papa (50°N and 145°W) andaveraged over all Januaries from the start of the Argo
program in the Gulf of Alaska in 2002 to the present time.
The temperature, salinity and density (σt) are colored red,green and black, respectively, and the horizontal lines
indicate the mean values computed from 2002 through2013. The final point shows the recently observed values
for January 2014, and the annotations indicate the value asa mean plus anomaly in standard deviations. The Argo
data verify the very large temperature departures seen inFigure 1a, with an anomaly of 4.4 standard deviations fromthe mean in temperature, and similar large deviations insalinity. We note that high temperature anomalies coupledwith low salinity anomalies both act to reduce density.
Hence we see very large anomalies in surface density thatmust act to impede mixing near Station Papa, and likely
over the entire region of SST anomaly.

In January 2014 (Fig. 1a), we see SST departures of 4.5
standard deviations or ~3°C from the long-term mean,centered on 42°N 148°W. The anomaly field covers a large
region of the N.E. Pacific in January 2014 and (not shown)a similar area in February, though the peak anomalies areslightly smaller. The black dots show the nominal locationsof the stations comprising Line-P, for later reference. The
authors of this article have never seen deviations fromnormal of 4.5 standard deviations before, despite extensive
work with the Line-P data set. The warming event first
appeared in November 2013, becoming strongest inJanuary (Fig. 1a), and lasting into February 2014.

To complete the description of the physical field, Figure 1cshows the distribution along Line-P of the temperature
anomaly fields in January 2014. The temperature field has
been computed using objective analysis to interpolate fromall Argo profiles available in a 10-day window centred on
the 15th day of January, and using a Gaussian covariancefunction with an e-folding scale of 400 km (see Brethertonet al., 1976, for a description of the methods). The meanstate used to compute the temperature anomalies is fromMarie Robert (Robert, 1994), which used all observations
from 1956 to 1991. The section in Figure 1c shows thevery strong warming and demonstrates that the event isprimarily restricted to the upper 100 metres of the watercolumn with possibly slight warming in deeper waters.
The equivalent plot for salinity (not shown) has a similar
behaviour with little influence below the top 100 metres.

Something as extraordinary as a 4.5-sigma deviation
requires corroboration, and for that purpose we examined
Argo data, which are not ingested by the Reynolds data sets.
The reason for this exclusion is that Argo floats sample
during their ascent phase, and the CTD pump is turned off

Fig. 1 Temperature and salinity in the N.E. Pacific in January 2014. Panel (a) shows the January 2014 SST anomalies (in standard deviations) from the
1982–2013 Reynolds NOAA/NCEP mean January state. Panel (b) shows January temperature (red), salinity (green) and density (σ t; black)departures from the 2002–2013 mean state (horizontal lines) at Ocean Station Papa. Panel (c) shows temperature anomalies (°C) contoured
versus depth and distance along Line-P in January 2014.

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PICES Press Vol. 22, No. 2

Fig.2

North Pacific Marine Science Organization(a) Sea surface temperature (SST) and 1000 mbar wind anomalies for January 2014 in the North Pacific Ocean. SST anomaly (color bar) andwind speed (arrow) scales are shown at bottom; plots are generated by the International Research Institute for Climate and Society, Columbia
University, NY on their website http://iridl.ldeo.columbia.edu using data from the NCEP/NCAR Reanalysis and the NOAA OISSTv2 dataset (Kalnay etal., 1996; Reynolds et al., 2007). The black rectangle outlines the region assessed in Panel b. (b)Average SeaWiFS and MODIS chlorophyll a forJanuary, as well as January 2014 MODIS chlorophyll, are plotted against latitude for the region between 140–150°W (data from the Giovanni
online data system, developed and maintained by the NASA GES DISC).

Wind anomalies (Fig. 2a) show the cause of the warm
anomalies in the ocean’s surface layer to be an unusual
flow from the south as the North Pacific high pressure cell
expanded northward. This pattern disrupted the path of thewesterly winds that cross the subarctic Pacific, winds that
normally transport nutrients from the subarctic North
Pacific into the subtropics during winter (Ayers and Lozier,2010; Whitney et al., 2013). In most years, a winter regionof high productivity is created by this Ekman transport
which reaches as far south as 30–32°N in the N.E. Pacific(Bograd et al., 2004). Named the Transition Zone
Chlorophyll Front (TZCF), it is an important feeding area
for migratory fish and seabirds (Block et al., 2011).

from the subarctic into the subtropics this past winter will
dramatically reduce the productivity of the eastern
subtropics over an area of ~17,000 km2 (20 Longitude 240 km northward displacement of the TZCF). One
possible outcome might be a northward shift of thealbacore tuna fishery in 2014.
References
Ayers, J. M., and M. S. Lozier (2010), Physical controls on theseasonal migration of the North Pacific transition zone
chlorophyll front. J. Geophys. Res. 115, C05001, doi:10.1029/
2009JC005596.
Block, B.A. et al. (2011), Tracking apex marine predator movements
in a dynamic ocean. Nature 475, 86–90, doi:10.1038/nature10082.
Bograd, S. J. et al. (2004), On the seasonal and interannual
migrations of the transition zone chlorophyll front, Geophys.
Res. Lett., 31, L17204, doi:10.1029/2004GL020637.
Bretherton, F. P., R. E. Davis, and C. B. Fandry (1976), A
technique for objective analysis and design of oceanic
experiments. Deep-Sea Res., 23, 559–582.
Kalnay, E. et al. (1996), The NCEP/NCAR 40-Year Reanalysis
Project. Bull. Amer. Meteor. Soc., 77, 437–471.
Reynolds, R. W. et al. (2007), Daily high-resolution blended
analyses for sea surface temperature. J. Climate, 20, 5473–5496.
Robert, M. 1994. A study of El Niño events along the British
Columbia coast. Department of Atmospheric and Oceanic
Sciences, McGill University, M.Sc. thesis.
Whitney, F. A., S. Bograd, and T. Ono (2013), Nutrient enrichmentof the subarctic Pacific Ocean pycnocline. Geophys. Res. Lett.
40, 1–6, doi:10.1002/grl.50439.

Without nutrients from the subarctic, the productivity ofsubtropical waters must decline. To assess impacts of thewarm anomaly on ocean productivity, satellite chlorophyll
between 140 and 150°W was averaged in 2 degree bins
between 20 and 50°N. South of the warm anomaly between
22 and 40°N, January chlorophyll a was well below theSeaWiFS (1998–2010) and MODIS (2003–2014) averages
in 2014 (Fig. 2b). Consequently, the TZCF (identified as
0.2 mg chl m–3) was located 240 km north of its average
location over the previous 16 years. Between 30–40°N,
surface chlorophyll dropped to 60% of the average values.
Top predators may be able to locate the chlorophyll front
since they are accustomed to travelling great distances intheir search for prey. However, weakened nutrient transport

Dr. Howard Freeland (Howard.Freeland@dfo-mpo.gc.ca) is a scientist emeritus at theInstitute of Ocean Sciences. Despite his retirement, he maintains a keen interest in the Argo
program and ocean climate change. (In this picture he is seen launching yet another Argo
float.)
Frank Whitney (whitneyf@shaw.ca) retired from Fisheries
and Oceans Canada in 2006. He has remained interested inchemical processes impacting the productivity of the ocean,
whether it is nutrient supply to surface waters or hypoxia at
depth. Recent papers (J. Oceanogr. 67: 481–492; GRL 40:1–6) summarized some of the trends he and colleagues
observed over a span of 25 years or more in the subarctic Pacific. (In this photo, Frank is studying acommon type of tube worm that barbecues quite nicely onboard ship.)Summer 201452