Seasonal variability of oceanographic conditions on the Pacific
continental shelf of the southern Baja California peninsula
O. Zaitsev*, C.J. Robinson** and O. Sánchez-Montante***
* Interdisciplinary Center of Marine Sciences, NacionalPolitechnical Institute, La Paz, Baja California Sur, 23096 Mexico.
** Institute of Marine Sciences and Limnology, Nacional Autonomous University of Mexico, D.F., Mexico
*** Center of Investigations in Applied Sciences and Advanced Technology, Politechnical Institute, Altamira, Tamaulipas, Mexico
Map and bathymetry of the study area
-116 -114 -112 -11022
24
26
28
118 116 114 112 110Longitude, W
22
24
26
28
30
32
Latit
ude,
N
B a j a C a l i f o r n i a
M e x i c o
P a c i f i cO c e a n
Gulf of California
Punta Eugenia
Ensenada
UlloaGulf
Magdalena Bay
Study area
• Area of interest is about 350 km long and up to 80 km wide.
• The Bahia Magdalena – Almejas lagoon system is located in the central part of the study area (24.5º N).
• A width of the continental shelf varies from 20-30 km (Magdalena lagoon system) to 70-80 km (Gulf of Ulloa).
• The average continental shelf gradient varies from 0.001 to 0.004. That of the continental slope from 0.03 to 0.06.
• The IMECOCAL grid of stations only covers the northern part of the Gulf of Ulloa.
Principal goals of the study
Seasonal variability of the thermal structure and circulation pattern on the continental shelf of the southern part of the Baja California peninsula
Can tropical and subtropical waters penetrate northward along the coast as far as Punta Eugenia?
Evaluation of upwelling intensity on the Pacific shelf of the southern part of the Baja California Peninsula.
Introduction
The most important forcing mechanism that affect both the California Current system and shelf circulation is wind stress.
Seasonally averaged sea surface wind in 2000.(PFEL/FNMOC data, www.pfeg.noaa.gov)
Jun-Mar 2001-05 Apr-Jun 2001-05
Oct-Dic 2001-05Jul-Sep 2001-05
8.1 m/s
7.6 m/s5.7 m/s
5.6 m/s20
24
28
32
20
24
28
32
124 W 120 116 112 108 124 W 120 116 112 -108
N
N
Left: Roden (1971) described for November 1969 the poleward flows of theTropical Surface Waters up to the Punta Eugenia and Equatorial Subsurface Waters along all the peninsula.
Right: Durazo and Baumgartner (2002) (CalCOFI and IMECOCAL data for 1997-99) assumed that during the El Niño years this northward advectionintensified, especially for Equatorial Subsurface Water at depth.
Data used
Averaged weekly and monthly SST distributions calculated fromAVHRR data for the period from 1996 to 2003 (provided by NOAA)
Sea height anomalies, calculated from altimetry data, and geostrophiccurrents calculated for a 10-day period using Ocean Circulation and Climate Advanced Model (OCCAM) model with Levitus climatology. These data are provided on the page of the NOAA/AOML/CoastWatchproject (www.aoml.noaa.gov/phod/ dataphod/work/trnanes/INTERFACE/index.html).
Averaged daily and monthly series of Coastal Upwelling Index (CUI) are provided on the PFEL Website (www.pfeg.noaa.gov).
Four hydrographic surveys (CTD) were made on board of R/V “El Puma”(March and December of 2003 and 2004) on the continental shelf in front of the Magdalena-Almejas lagoon system.
Three CTD transects were made in Apr 2000, Feb 2001 and Apr 2002in front of the main inlet of Magdalena Bay.
Average monthly SST anomalies for the period from 1996-2003(AVHRR data)
Sea height anomalies (SHA) calculated from satellite altimetry data
(NOAA/AOML/Coast Watch data)
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Oct 2006
-32
-24
-16
-8
0
8
16
24
32
40
H, cm
-120 -118 -116 -114 -112 -11022
24
26
28
30
32Apr 2006
Average seasonal geostrophic currents calculated from SHA using the OCCAM model with the Levitus climatology
for the period from 2003 to 2006(NOAA/AOML/Coast Watch data)
Jan-Mar Apr-Jun
22
23
24
25
26
27
28 Jan-Mar
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Scale (cm/s)
125
Apr-Jun
-116 -114 -112 -110
Scale (cm/s)
125
Average seasonal geostrophic currents calculated from SHA using the OCCAM model with the Levitus climatology
for the period from 2003 to 2006(NOAA/AOML/Coast Watch data)
Jul-Sep Oct-Dec
-116 -115 -114 -113 -112 -111 -110 -10922
23
24
25
26
27
28 Jul-Sep
Scale (cm/s)
125
-115 -114 -113 -112 -111 -110 -109
Oct-Dec
Scale
125
Seasonal cycle of off-shore Ekman transport, with 0.5 latitude resolution, for entire Pacific coast (left) and for the latitude of
the Magdalena bay (right), calculated using PFEL methodology.
Units are metric tons per second per 100 m coastline.
Jan Feb Mar AprMay Jun Jul Aug Sep Oct NovDec0
20
40
60
80
100
120
CU
I, m
3 s-
1 / 1
00 m
1 2 3 4 5 6 7 8 9 10 11 12Month
23
24
25
26
27
28
29
30
31
32
Latu
tude
a
Typical SST anomaly at the latitude of Magdalena Bay (April 2002)
-112.4 -112.2 -112.0 -111.8 -111.6 -111.424.2
24.4
24.6
24.8
25
25.2
SST AnomalyApril, 2002. AVHRR data. 24.5° N.
Longitude
Latit
ud
Comparison of Coastal Upwelling Index (CUI) with difference in SST between the upwelling zone and the adjacent sea.
-113 -112
24
25Maximum UpvellingZone
Adjacent Zone
Pacific ocean
BM
PeninsulaBaja California
60 km
200 misobath
-2
0
2
4
SST
Dife
renc
e (º
C)
-80
-40
0
40
80
120
160
CU
I (m
3 s-1
/ 1
00 m
)
-4
0
4
SST
Ano
maly
(ºC)
5
10
15
20
25
30
SST
(ºC)
1996 1997 1998 1999 2000 2001
SST CUI
1996 1997 1998 1999 2000 2001
Sampling grid used during the 2000-2004 surveys(R/V “El Puma”, hydrographic boats).
BM
112.6W 112.4W 112.2W 112W 111.8W 111.6W 111.4W 111.2W24N
24.2N
24.4N
24.6N
24.8N
25N
Apr00Apr02Feb01
Dec04Mar04Dec03Mar03
Typical stratification patterns in front of Magdalena Bay in Spring (Mar 2003)
24.4 24.8 25.2 25.6 26 26.4 26.8Sigma-t
-200
-160
-120
-80
-40
0
Dep
th, m
24.4 24.8 25.2 25.6 26 26.4Sigma-t
-200
-160
-120
-80
-40
0
a b
BM
112.6W 112.4W 112.2W 112W 111.8W 111.6W 111.4W 111.2W24N
24.2N
24.4N
24.6N
24.8N
25N
Mar03
b
a
Field observations of the coastal upwelling pattern in front of Magdalena Bay in March 2003
0 5 10 15 20 25 30 35150
120
90
60
30
0
Dep
th, m
0 5 10 15 20 25 30 35150
120
90
60
30
0
Dep
th, m
Salinity
Temperature,
33.93434.134.234.334.434.534.6
1112131415161718
oC
Comparision between TS- diagrams in the Spring and Fall (2003 data).
33.5 34 34.5 355
10
15
20
25
Tem
pera
ture
SAW
StSW
ESsW
TrW
200 m
100 m
0 m
33.5 34 34.5 35Salinity
5
10
15
20
25
SAW
StSW
ESsW
TrW
200 m
100 m
0 m
March 2003 December2003
Concluding remarks
Analysis of the 2001-06 data shows that, from January to June, relatively cold and low salinity waters (TrW and sometimes SAW) are present on the continental shelf in front of the Magdalena lagoon system.
In Summer and Fall, subtropical surface water (StSW), eastern tropical Pacific waters(TSW) and, ocasionally, Equatorial subsurface Water (EsSW) penetrate along the coast northward as far as Punta Eugenia, including the continental shelf in front of Magdalena bay.
Inspite of relatively low upwelling intensity (CUI<130 m**3/s/100m)in the southern part of the peninsula, the favorable bottom topography provokes a well-developed upwelling pattern in SST distributions over the continental shelf, including the area in front of the Magdalena Bay.
Thank you.