long term changes in coastal upwelling
*
garcia-reyes ,
marisol
john largier
bodega marine lab - uc davis
epoc ‘08
bakun hypothesis
- “global greenhouse warming should lead to intensification of the continental thermal lows adjacent to upwelling regions. this intensification would
be reflected in increased onshore-offshore atmospheric pressure gradients, intensified alongshore
winds, and accelerated coastal upwelling circulation” that would result into cooling of the ocean
surface1.
27
22
14
13
26
12
42
data
28
- hourly wind speed, wind direction and SST data
from NDBC buoys along california. 1980-2007
- wind speed component along its principal axis
at each location, as upwelling forcing
- daily and monthly means, standard deviation
and trends.
11
23
25
buoy
monthly trends
the monthly means trends show stronger upwelling-favorable winds and a decreasing SST between 35-39N, except in monterey bay. the upwelling
index show an increment (negative trend in the figure) for the same latitudes, consistent with bakun hypothesis. this region corresponds with the
strongest winds along california and it’s also where the upwelling process dominates the coastal conditions. these trends are consistent with previous
works. 3, 2, 6, 7, 8
the wind is weaker in the north, as well as the upwelling index, but the SST data presents different trends for buoys 27 & 22, which could result from
the geography of the area. in the south wind trends are not consistent with the observed cooling, but this could be an effect of the geography as well.
previous works 3,4,5,6 showed warming trend in southern california, but the used time series differ from the buoys’ in their location: calcofi uses a crossshore transect that includes water from the california current and the shore stations data sample shallow water. both data sets are consistent with
global temperature increment. the buoy samples are from the upwelling region, where the conditions are dominated by the upwelling.
Type to enter text
local upwelling intensity
an indicator is calculated by averaging the upwelling favorable wind speed for the days
when wind is stronger and SST is colder than selected thresholds for each location. it is an
indicator of the persistence & intensity of the upwelling. the upwelling intensity trend is
negative for most locations, suggesting that the upwelling events are enhanced.
the number of days both conditions are met indicates the persistence of the upwelling
events, but it does not resolve between longer season, longer events or more recurrent
events. in central california the number of days increases, except for monterey bay. therefore, in central california, upwelling favorable winds are stronger and are present more
days per year.
the trend of confidence intervals for the wind and SST data shows an increased variability
in the wind speed magnitude. however, the SST does not show a similar trend for all locations.
the chlorophyll concentration from satellite imagery and calcofi data also shows a postive trend in the coastal region, in particular in central california (suryan, personal communication).
references
1. venrick, 1987.
7. snyder, 2003.
2. bakun, 1990.
8. dilorenzo, 2005.
3. schwing, 1997.
9. greeg, 2005.
4. roemmich. 1995
10. auad, 2006.
5. mcgowan, 1998.
11. chavez
upwelling season timing
the wind speed trend of each month shows weaker
winds in february in central and south california, but enhanced winds in march for central california.
stronger winds are observed in september and october, mostly in central california, with a decrease in SST
for all locations for the same months. this suggests that
the upwelling season is longer.
the upwelling intensity also points out the beginning and
end of the upwelling season. the beginning of upwelling doesn’t show a similar trend along the coast. however, the start of the upwelling season is not determined
only by the wind but also by the oceanographic conditions in the first month of the year. on the other hand, in
central california the upwelling season seems to be
larger, except for monterey bay & bodega bay.
6. mendelssohn, 2002
12. bograd, 2008.
this work is in part supported by the NSF under Awards No. ATM-0619139
contact:
*
solgarcia@ucdavis.edu