CRUISE REPORT S213 Scientific data collected aboard SSV Robert C. Seamans San Diego, California – La Paz, Baja California Sur – Puerto Vallarta, Mexico 11 October – 17 November, 2007 Jumbo flying squid (Dosidicus gigas ) hooked near Cerralvo Island. White portion of lure is 10cm in length. Photo by Chief Scientist Jeff Schell Sea Education Association Woods Hole, Massachusetts
60
Embed
CRUISE REPORT S213 Scientific data collected aboard SSV … · 2013. 5. 16. · CRUISE REPORT S213 Scientific data collected aboard SSV Robert C. Seamans San Diego, California –
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
CRUISE REPORT S213
Scientific data collected aboard SSV Robert C. Seamans
San Diego, California – La Paz, Baja California Sur – Puerto Vallarta, Mexico
11 October – 17 November, 2007
Jumbo flying squid (Dosidicus gigas) hooked near Cerralvo Island. White portion of lure is 10cm in length.
Photo by Chief Scientist Jeff Schell
Sea Education Association
Woods Hole, Massachusetts
Contact Information: Dr. Jeffrey M. Schell Sea Education Association P.O. Box 6 Woods Hole, MA 02543 508-540-3954 (phone) 800-552-3633 (phone) 508-457-4673 (fax) www.sea.edu
This document should be cited as:
Schell, Jeffrey, M. 2008. Final report for S.E.A. cruise S213. Sea Education Association, Woods Hole, MA 02540. www.sea.edu.
To obtain unpublished data, contact the Chief Scientist or SEA data archivist:
Figure 2a-b Surface plots of a) temperature and salinity, b) density and fluorescence
8-9
Table 2
Summary of oceanographic sampling stations 10-13
Table 3 Surface Station data 14-15
Figure 3a-b Surface plots of a) nutrients and b) estimates of productivity
16-17
Table 4
CTD station data 18
Figure 4 T-S plots for select CTD stations 19
Figure 5a-b Dissolved oxygen and in situ chlorophyll-a fluorescence profiles for select CTD stations
20
Figure 6 Temperature, salinity and dissolved oxygen cross-section plots for entire cruise track
21
Table 5
Hydrocast station data 22-26
Figure 7 Surface current magnitude and direction for entire cruise track
27
Figure 8a-c Regional examples of surface and sub-surface current features along the cruise track
28-30
Figure 9 Echo amplitude and influence on ADCP sensitivity and measurement errors
31
Island Mass Effect Rationale and Sample Description
32
Figure 10 Sampling Plan for Catalina Island and Mass Effect Indices (MEIs)
33
Figure 11-a-d Catalina Island data: a) Surface Current vector plot, b-d) Hydrographic cross-section plots for island transects
34-37
Figure 12 Sampling Plan for Isla de Guadalupe and Mass Effect Indices (MEIs)
38
Figure 13-a-d Isla de Guadalupe data: a) Surface Current vector plot, b-d) Hydrographic cross-section plots for island transects
39-42
2
Figure 14 Sampling Plan for Isla Socorro and Mass Effect Indices (MEIs)
44
Figure 15a-c Isla Socorro data: a) Surface Current vector plot, b-d) Hydrographic cross-section plots for island transects
45-46
Table 6 Shipek grab station data for island mass effect study
47
Table 7 Neuston tow station data 48-49
Table 8 Meter net station data 50
Table 9 Tucker trawl station data 51-52
Table 10 Squid jigging station data 53
Figure 16 Eastern Pacific oxygen minimum zone (OMZ) and rationale for Trophic Dynamic study
54
Figure 17 Zooplankton and Myctophid distribution in relation to OMZ
55
Table 11 Qualitative description of shipek grab station data
56
Table 12 Student research topics for cruise S213 57
References 58
3
Table 1. S213 Ship’s crew and student participants Nautical Staff Jeremy Law Captain Jullie Jackson Chief Mate Nate Darling 2nd Mate Jay Amster 3rd Mate Dave Reynolds Engineer James Joslin Assistant Engineer Maggie McCullough Steward Scientific Staff Jeff Schell Chief Scientist Skye Morét 1st Scientist Austen Thomas 2nd Scientist Katie Hammond 3rd Scientist Scientific Observers Raymundo Avendaño CICIMAR professor Andres Levy CICIMAR professor Students Tasia Blough Roger Williams University Emily Cira Boston University Marjorie Crowley Villanova University Delia Daza Community College of Rhode Island K. Aspen Gavenus Bowdoin College Timothy Groves Colorado College Rebecca Inver Long Island University - Brooklyn Ellie Kane University of Pennsylvania D. Folasade Morvan University of Maryland Lucy Rozansky Colorado College Shiloh Schlung Boston University Isaac Schoepp Valparaiso University Katie Shaughnessy Northeastern University Adam Smith Florida Gulf Coast University Thomas Stout Colorado College Kristine Unkrich Whitman College
4
Data Description This cruise report provides a record of data collected during S213 aboard the SSV Robert C.
Seamans from San Diego, California to Puerto Vallarta, Mexico (Figure 1a) with a stop at La Paz on the
southeastern shore of Baja California Sur. We collected samples or data with 123 individual deployments
from 79 discrete stations (Table 2) along our cruise track. In addition we continuously sampled water
depth, sub-bottom profiles and Acoustic Doppler Current Profiles (ADCP) along with flow-through sea
surface temperature, salinity and in vivo chlorophyll-a fluorescence.
This report summarizes physical, chemical and biological characteristics along our cruise track
and around surveyed island systems. The S213 cruise track traversed several oceanic regions that can be
distinguished by their sea surface temperature, salinity, density and fluorescence values (Figures 1b, 2a-
b). Discrete surface water characteristics (T, S, nutrients, productivity estimates) were sampled
periodically (36 stations) along the cruise track (Figure 3a-b, Table 3). Sub-surface water masses and
their chemical properties were also surveyed using a CTD and 12 bottle carousel (Tables 4 and 5).
Regional differences in hydrography can be seen in T-S plots (Figure 4), vertical profiles of dissolved
oxygen and chlorophyll-a fluorescence (Figure 5a-b) and contour plots of temperature, salinity and
dissolved oxygen (Figure 6). Patterns of surface and sub-surface currents were complex. Large-scale,
slow recirculation intuited a posteriori from SST satellite images was masked by smaller scale circulation
associated with eddies and coastal filaments (Figures 7, and 8a-c). Resolution of weak current flow was
also hampered by considerable diel vertical migration of the planktonic community (Figure 9).
The expression (distribution of nutrients, estimates of primary productivity, and zooplankton) and
underlying mechanisms (terrestrial runoff, wind and current-driven upwelling) of island mass effect were
examined in detail around Catalina Island (Figure 10 and 11a-d), Isla Guadalupe (Figure 12 and 13a-d)
and Isla Socorro (Figure 14 and 15a-c). Regions with the greatest expression of island mass effect more
often corresponded with regions of terrestrial runoff (based on shelf sediments characteristics) and less so
with any forms of upwelling (Table 6). Qualitative description of shelf sediments are detailed later in the
report (Table 11).
The distribution of neuston net, meter net, and Tucker trawl stations and corresponding
zooplankton and micronekton measures along with numbers of select nekton species are presented
(Tables 7-9). Additional biological sampling for juvenile and adult jumbo squid (Dosidicus gigas) was
also conducted using various squid jigs, rod and reel and visual observation (Table 10). Influence of the
5
oxygen minimum zone on regional and vertical distributions of collected organisms was examined; and
implications for regional trophic dynamics were explored (Figures 16 and 17).
Additional CTD, CHIRP, ADCP and biological data not reported here are available on request
through Sea Education Association (SEA) and the Chief Scientist. The information in this report is not
intended to represent final interpretation of the data and should not be excerpted or cited without written
permission from SEA.
As part of SEA’s educational program, undergraduates conducted independent oceanographic
research during the cruise. Project explored regionally, relevant topics in the disciplines of physical,
chemical, biological and geological oceanography (Table 12). Student research efforts culminated in a
written report and public presentation to the ship’s company. These papers are available on request from
SEA.
Oceanographic Setting
Atmospheric and oceanic conditions across the equatorial Pacific Ocean during the Fall 2007
reflected a transition from weak, but persistent El Nino conditions to developing La Nina conditions
(http://www.bom.gov.au/climate/enso/ ). August through November, Southern Oscillation Index (SOI)
values in 2006 (cruise S207) were: -15.9 / -5.1 / -15.3 / -1.4. For cruise S213, SOI values for the same
period were: 2.7 / 1.5 / 5.4 / 9.8. Hydrographic conditions during S213 were markedly different from
conditions experienced during S207. The S207 report is available upon request.
Jeff Schell Chief Scientist S213
6
Figure 1a. Final cruise track for S213 based on hourly (local time) positions. Oceanic biomes recognized during S213 include Southern California Bight (SCB), Pacific Sub-arctic Water brought in by the California Current (CC), North Pacific Central Water (NPCW), Gulf of California (GC) and North Pacific Equatorial Water (NPEW). Extensive coastal surveys were conducted around Santa Catalina Island, Isla de Guadalupe and Isla de Socorro.
San Diego
La Paz
Puerto Vallarta
Catalina
SCB
CC
Guadalupe
NPCW
NPEW
GC
Socorro
NPCW
San Diego
La Paz
Puerto Vallarta
Catalina
SCB
CC
Guadalupe
NPCW
NPEW
GC
Socorro
NPCW
7
Figure 1b. General hydrographic setting during S213. S213 cruise track (white line) overlays SST blended product (8-day composite, 0.1° resolution centered at 15 October 2007) from NOAA – Ocean Watch Live Access Server (http://las.pfeg.noaa.gov/oceanWatch/ ). Typical of western boundary currents the California Current exhibits weak, meandering circulation. However, subduction of this cold, less saline water beneath NPCW can be observed as far south as Isla de Guadalupe. Possibly due to the onset of La Niña NPEW water is confined south of the Baja peninsula. Significant influx of NPCW from the west creates complex circulation along coastal upwelling regions and has measurable effects on the SCB region. These described hydrographic conditions are in stark contrast to observed conditions in 2006 (see S207 Cruise Report) during a weak, but persistent El Niño.
San Diego
La Paz
Puerto Vallarta
Catalina
SCBCC
Guadalupe
NPCW
GC
Socorro
NPCW
NPEW
San Diego
La Paz
Puerto Vallarta
Catalina
SCBCC
Guadalupe
NPCW
GC
Socorro
NPCW
NPEW
8
Figure 2a. Surface plots of temperature and salinity for S213. Recognized water masses were the California Current moving south, North Pacific Equatorial Water (NPEW) moving north, the Gulf of California Water circulating within the basin and a large transition region of mixed water masses with significant influences of North Pacific Central Water (NPCW) intruding from the west. Note the significant entrainment of NPCW in the general SCB recirculation leads to unusually high salinity in the region of the CC.
CC
NPCW
NPEW
GC
NPCW
CC
NPCW
NPEW
GC
NPCW
9
Figure 2b. Surface plots of density and fluorescence for S213. Recognized water masses were the California Current moving south, North Pacific Equatorial Water (NPEW) moving north, the Gulf of California Water circulating within the basin and a large transition region of mixed water masses with significant influences of North Pacific Central Water (NPCW) intruding from the west. Note the low fluorescence values thorough out the central portion of the cruise track associated with NPCW.
CC
NPCW
NPEW
GC
NPCW
CC
NPCW
NPEW
GC
NPCW
10
Table 2. Station summary of oceanographic sampling for S213.
Station # (S213-)
Date (2007)
Time (local +8 GMT)
Log (nm) Lat (dec Deg N)
Lon (dec Deg W)
Location Station Type
001 12-Oct 2121 14 32.49 -117.29 Southern CA Bight SJ 002 13-Oct 0121 15 32.47 -117.29 Southern CA Bight NT 003 13-Oct 1148 52 33.00 -117.66 Catalina Island CTD 004 13-Oct 2133 62 33.01 -117.54 Southern CA Bight SJ 005 14-Oct 0848 103 33.35 -118.31 Catalina Island SG 006 14-Oct 0949 103 33.41 -118.38 Catalina Island MN 007 14-Oct 1158 104 33.40 -118.36 Catalina Island CTD 007 14-Oct 1134 104 33.40 -118.36 Catalina Island SG 008 14-Oct 1650 120 33.45 -118.32 Catalina Island CTD 008 14-Oct 1650 120 33.45 -118.32 Catalina Island HC 009 15-Oct 1026 161 33.58 -118.80 Catalina Island CTD 009 15-Oct 1026 161 33.58 -118.80 Catalina Island HC 010 15-Oct 1957 174 33.53 -118.67 Catalina Island CTD 010 15-Oct 1820 173 33.50 -118.69 Catalina Island MN 011 15-Oct 2131 177 33.48 -118.63 Catalina Island CTD 011 15-Oct 2208 177 33.47 -118.63 Catalina Island SG 012 15-Oct 2355 182 33.38 -118.57 Catalina Island CTD 012 15-Oct 2355 182 33.38 -118.57 Catalina Island HC 013 16-Oct 0347 182 33.39 -118.55 Catalina Island CTD 013 16-Oct 0225 186 33.39 -118.53 Catalina Island MN 014 16-Oct 0520 186 33.40 -118.51 Catalina Island CTD 014 16-Oct 0550 186 33.40 -118.51 Catalina Island SG 015 17-Oct 1010 332 31.10 -119.70 PSAW-California
Current CTD
015 17-Oct 1151 332 31.11 -119.66 PSAW-California Current
NT
016 17-Oct 2037 362 30.69 -120.06 PSAW-California Current
TT
017 18-Oct 0006 371 30.71 -120.11 PSAW-California Current
NT
018 18-Oct 1020 431 30.18 -121.07 PSAW-California Current
CTD
018 18-Oct 1020 431 30.18 -121.07 PSAW-California Current
HC
018 18-Oct 1020 431 30.18 -121.07 PSAW-California Current
SD
019 18-Oct 2014 469 29.74 -121.63 PSAW-California Current
CTD
019 18-Oct 0000 469 29.74 -121.63 PSAW-California Current
SJ
020 19-Oct 0021 480 29.69 -121.33 PSAW-California Current
NT
021 19-Oct 1123 530 29.59 -120.33 PSAW-California Current
Duplicate station numbers refer to different oceanographic equipment that was either deployed concurrently in the same location or was deployed sequentially in the same general location once the vessel was hove to. The General Location for stations has been categorized by position relative to nearest island (Santa Catalina, Guadalupe, Socorro ), or oceanic biome (Southern California Bight, California Current, North Pacific Central Water, Gulf of California and North Pacific Equatorial Water). Abbreviations for type of oceanographic equipment deployed: HC – 12 niskin bottle hydrocast, NT – neuston tow, PN – phytoplankton net, MN – meter net (either 1 or 2 m diameter), CTD – conductivity, temperature and depth profiler, HC – hydrocast with 12 Niskin bottles, SD – secchi disc, SG – shipek grab, SJ – squid jigging, Styro – styrofoam-cup cast, and TT – Tucker trawl.
Surface water samples were collected using a clean, seawater flow-thru system (intake ~ 1-3m depth) with in-line temperature, salinity and in vivo chlorophyll-a, fluorescence sensors. Discrete water samples were collected for phosphate (PO4) analysis, measured by colorimetric analysis with an Ocean Optics Chem2000 digital spectrophotometer, and extracted chlorophyll-a (Chl-a) concentrations, measured with a Turner Designs Model 10-AU Fluorometer following methods outlined in Parsons, Maita and Lalli (1984; A Manual of Chemical and Biological Methods for Seawater Analysis, Pergamon Press). Chlorophyll-a samples were filtered through 0.45 µm filters. A blank space indicates that no sample was collected for that analysis. Sample concentrations below detectable limits are indicated as “BD”.
16
Figure 3a. Surface plots of phosphate and nitrate from discrete Surface Stations for S213. Recognized water masses as described in Figure 2. Parameter measurements as described in Table 3. Note the different patterns of nutrient distribution showing phosphate concentrations highest in NPCW, whereas nitrate concentrations are highest near shore. Source of surface nutrients may account for these differences. Coastal run-off may supply a disproportionate amount of nitrogen to surface waters allowing phosphate concentrations to be drawn down by increased productivity. In contrast, periodic upwelling processes at offshore locations may be nitrate limited due to a shallow oxygen minimum zone. Low oxygen conditions can limit nitrification processes.
CC
NPCW
NPEW
GC
NPCW
CC
NPCW
NPEW
GC
NPCW
17
Figure 3b. Surface plots of extracted chlorophyll-a and in vivo fluorescence from discrete Surface Stations for S213. Recognized water masses as described in Figure 2. Parameter measurements as described in Table 3. Note the low estimates of surface water productivity associated with NPCW and NPEW and higher estimates associated with coastal regions. Surprisingly, these estimates of productivity do not follow patterns of surface nutrients. One explanation is that NPCW waters are nitrogen limited, allowing phosphate concentrations to accumulate in surface waters.
Figure 4. T-S profiles from select CTD casts for S213. Oceanographic regions identified: Blue (CC) – California Current [cold and less saline], Green (SCB) – Southern California Bight /Catalina Island, and note similarity with Red (NPCW) – North Pacific Central Water, Orange (NPEW) – transition to North Pacific Equatorial Water [warming and increasing salinity], and Black (GC) – Gulf of California Water [warm and high salinity].
20
Figure 5 a and b. Dissolved oxygen and in situ chlorophyll-a fluorescence profiles from select CTD casts for S213. Oceanographic regions identified: Colors and abbreviations as in Figure 4. Vertical scales differ in each graph. Note the shallow oxygen minimum zone of NPEW and GC water and low values of the deep fluorescence maximum layer in NPCW.
21
Figure 6. Temperature, salinity and dissolved oxygen cross-section plots for S213. Distance (km) along x-axis follows the cruise track from San Diego, CA, USA to Puerto Vallarta, MX. Oceanographic features identified: abbreviations as in Figure 4. Note the narrow, surface aspect of the CC, but more significant expression as a cold, less saline layer subducted beneath NPCW. Data interpolation by VG Gridding in ODV, 10 x-scale and 70 y-scale.
Water samples were collected in 2.5 liter Niskin bottles deployed on a self-contained carousel system with a SBE-019Plus CTD sensor (Seabird Instruments, Inc.). Dissolved oxygen (O2) concentrations were determined using an in situ sensor (Seabird Instruments Inc.). Phosphate (PO4), and nitrate (NO3) levels were measured by colorimetric analysis with an Ocean Optics Chem2000 digital spectrophotometer. Chlorophyll-a (Chl-a) concentrations were determined with a Turner Designs Model 10-AU Fluorometer following methods outlined in Parsons, Maita and Lalli (1984; A Manual of Chemical and Biological Methods for Seawater Analysis, Pergamon Press). Chlorophyll-a samples were filtered through 0.45 µm filters. A blank space indicates that no sample was collected for that analysis. Sample concentrations below detectable limits are indicated as “BD”.
27
Figure 7. Current magnitude and direction surface plots for S213. Currents were measured using a hull-mounted ADCP – acoustic doppler current profiler (75 kHz, RDI Ocean Surveyor) with a surface offset of 18m. Surface circulation along the cruise track was not characterized by a predominate current; instead, flow was generally weak (= 500 mm/s or ~1.0 knot) and complex, being composed of mesoscale eddies, recirculations and coastal filaments. Cross-section magnitude and direction plots from Regions A and B will highlight these features. On a more localized scale, stronger currents were evident around islands and will be highlighted in subsequent figures.
A
B
A
B
28
Figure 8a. Current magnitude and direction (N-S) surface and cross-section plots for Region A (see Figure 7). Currents with a minimum magnitude of 250mm/s or a 0.5 knot are shown. Numerous eddies of varying dimension (width and depth) can be observed offshore Punta Eugenia.
29
Figure 8b. Current magnitude and direction (E-W) surface and cross-section plots for Region B (see Figure 7). Currents with a minimum magnitude of 250mm/s or a 0.5 knot are shown. Numerous eddies of varying dimension (width and depth) can be observed. Note, periodically the ADCP recorded a false bottom, indicated by disproportionately strong and highly, irregular current magnitudes. These regions are indicated by a grey-shaded overlay. These false bottoms were coincident with low echo amplitudes associated with vertical migration of plankton (see Figure 9).
30
Figure 8c. Current magnitude and direction (N-S) surface and cross-section plots for Region B (see Figure 7). Currents with a minimum magnitude of 250mm/s or a 0.5 knot are shown. Numerous eddies of varying dimension (width and depth) can be observed. Note, periodically the ADCP recorded a false bottom, indicated by disproportionately strong and highly, irregular current magnitudes. These regions are indicated by a grey-shaded overlay. These false bottoms were coincident with low echo amplitudes associated with plankton migrations (see Figure 9).
31
Figure 9. Echo amplitude and current magnitude cross-section plots for Region B (see Figure 8c). In this east-west transect through NPEW diel patterns of plankton vertical migration were clearly evident. Interestingly, the corresponding dearth of suspended particles below 200m led to errant readings by the ADCP; which may at first appear to register as false –bottom readings.
False Bottom readingsFalse Bottom readings
32
Island Mass Effect Study – Rationale and Sample Description Island mass effect is an increase in productivity near an island in comparison to the
surrounding oceanic region (Dandanneau and Charpy 1985). This increased productivity hypothetically promotes increased abundance of secondary consumers (zooplankton) which in turn support higher trophic levels and fisheries resources (Hernandez-Leon 1991). The chemical processes that support the development of a mass effect are linked to the physical processes of upwelling (Wolanski and Hamner 1988); as well as local effects of terrestrial runoff (Martinez and Maamaatuaiahutapu 2004, Messie et al 2006).
Upwelling around islands can be driven by prevailing winds and ekman transport of surface waters offshore. An alternate, though not mutually exclusive process of upwelling can occur when prevailing surface currents impinge upon an island from one direction and form eddies and localized upwelling in the wake of said island. Whether wind-driven or current driven upwelling processes manifest themselves around an island both are a function of local bathymetry, prevailing wind and current patterns and the characteristics of deep water being brought to the surface (Wolanski and Hamner 1988). A comparison of the geologic, physical, chemical and biological setting of Santa Catalina, Guadalupe and Socorro islands provides an unparalleled opportunity to understand the geologic setting and oceanographic processes that determine the occurrence and expression of island mass effects. Such an understanding can inform fisheries resource management by identifying the location and seasonality (wind-driven or current driven) of a mass effect and the extent to which a local food web is enhanced. Sampling collection was designed to reveal the following:
• Location and expression of island mass effect o Surface Stations (nutrients, fluorescence, extracted chlorophyll-a) o oblique towed 1-Meter Net plankton tows
• Location and origin of upwelling (either wind-driven or current eddies) o CTD and ADCP transects
• Location of terrestrial runoff o Shipek Grab sediment samples o Sorting and Reflectivity measurements
Figure 10. Sampling plan for Catalina Island – Mass Effect study. Location of CTD stations (blue dots) and orientation of cross section plot transects (red arrow) are shown. Stations occurred on 14-16 October, 2007. Island coastline (dark outline) is overlaid from a hand-drawn USGS nautical chart. Light grey island coastline indicates the poor representation of island position using ODV coastlines. For each transect, the localized mass effect was estimated using surface stations from inshore and offshore locations. The following parameters were measured: PO4 concentration (µM), in vivo chlorophyll-a fluorescence (volts), extracted chlorophyll-a (µg/l); and from 0-200m oblique 1-meter net (335um) plankton tows that occurred mid-transect: zooplankton density (ml/m3), zooplankton diversity (H’), gelatinous zooplankton density (ml/m3) and mickronekton density (ml/m3). For ease of comparison island mass effect parameters were transformed into equivalent units in the following manner: all parameters are plotted as proportion of maximum value (range 0.0-1.0) for each island; these are collectively referred to as Mass Effect Indices (MEI’s).
33
Figure 10. The island mass effect was most prominent along the North Transect having 7 of the highest ranking MEIs (out of 10).
Figure 11 a-d. Surface Current vector plot and Temperature, salinity, density and fluorescence cross-section plots for three inshore-to-offshore transects around Santa Catalina. Location and depth of CTD casts are shown by dashed lines in cross-section plots. Depth scale has been limited to upper 200m to emphasize surface features, though CTD casts frequently reached 1000 meters or more. Data interpolation by VG Gridding in ODV, 350 x-scale and 30 y-scale was used to help elucidate sloping isolines for each parameter. Temperature range 5-20 °C, salinity range 33.2-34.2 psu, density (s -t) 24-27 kg/m3, chlorophyll-a fluorescence 0.0-0.6. a) Surface Current vector plot. Note presence of an anti-cyclonic current eddy along the eastern transect and strong current shear (though no eddy feature could be resolved) along the northern transect.
35
b) East Transect. Based on isolines there is no indication of wind-driven upwelling (upward sloping of isolines toward shore – left side of graph) or eddy–driven upwelling (upward doming of isolines). Chlorophyll-a fluorescence shows a surface peak nearshore and an offshore, sub-surface maximum.
36
c) North Transect. Based on isolines there is no indication of wind-driven, coastal upwelling but there is some indication of sloping isopycnals offshore, possibly associated with an edge of an anti-cyclonic eddy (though this feature is not fully resolved in the surface current plot, Figure 11a). Chlorophyll-a fluorescence is minimal nearshore but shows a significant offshore, sub-surface maximum, coincident with sloping isopycnals.
37
d) West Transect. Based on isolines there is no indication of wind-driven upwelling or eddy–driven upwelling. Chlorophyll-a fluorescence shows a weak, sub-surface maximum compared to other island transects.
38
Figure 12. Sampling plan for Isla de Guadalupe – Mass Effect study. Location of CTD stations (blue dots) and orientation of cross section plot transects (red arrow) are shown. Stations occurred on 20-23 October, 2007. Island coastline (dark outline) is overlaid from a hand-drawn USGS nautical chart. Light grey island coastline indicates the poor representation of island position using ODV coastlines. Analysis of island Mass Effect Indices (MEIs) as in Figure 10. Note, there were no Surface Station samples for the East Transect (ns), consequently the North Transect has a majority of high ranking MEIs for nutrient and productivity estimates. Conversely, the East transect had the highest ranking MEIs for 3 of the 4 zooplankton MEIs.
Figure 13 a-d. Surface Current vector plot and Temperature, salinity, density and fluorescence cross-section plots for three inshore-to-offshore transects around Isla de Guadalupe . Location and depth of CTD casts are shown by dashed lines in cross-section plots. Depth scale has been limited to upper 200m to emphasis surface features, though CTD casts frequently reached 1000 meters or more. Data interpolation by VG Gridding in ODV, 250 x-scale and 30 y-scale was used to help elucidate sloping isolines for each parameter. Parameter ranges as in Figure 11. a) Surface Current vector plot. Along the entire eastern shore of Guadalupe there is a
prevailing southerly current showing considerable shear with the island. The result is the appearance of significant recirculation and eddy formation along the southern shore.
40
b) North Transect. Sloping isolines suggest downwelling along the coast, but also a shallow and weakly stratified water column offshore. Both were consistent with the persistent northerly winds at that were responsible for the prevailing surface currents at this time (previous figure). A significant offshore, surface maximum in fluorescence, as well as a uniformly distributed sub-surface maximum, coincided with the weakened stratification.
41
c) East Transect. Isolines suggest increased stratification and possible downwelling in comparison to the Northern transect. Diminished surface fluorescence coincides with this change in hydrographic conditions.
42
d) South Transect. A deeper and more steeply stratified water column along the South Transect was consistent with the weak sub-surface fluorescence maximum layer.
43
Figure 14. Sampling plan for Isla de Socorro – Mass Effect study. Location of CTD stations (blue dots) and orientation of cross section plot transects (red arrow) are shown. Stations occurred on 10-11 November, 2007. Island coastline (dark outline) is overlaid from a hand-drawn USGS nautical chart. Analysis of island Mass Effect Indices (MEIs) as in Figure 10. Both transects surveyed around Isla de Socorro showed significant island mass effects, and had similar values for nearly all MEIs, with the notable exception of micronekton density. Patterns in diel migration may account for this difference (see Table ??). However, this explanation would not be consistent with observed similarities in zooplankton indices among the two transects.
Isla de Socorro Island Mass EffectIndices
PO
4 in
shor
e
Flu
or in
shor
e
Chl
-a in
shor
e
Zoo
Den
Zoo
Div
Gel
Den
Mne
k D
en
PO
4 of
fsho
re
Flo
ur o
ffsho
re
Chl
-a o
ffsho
re
Legend
0.00
0.50
1.00
Socorro_east
0.00
0.50
1.00
Socorro_west
0.0
19.0 oN
18.8 oN
18.6 oN
111.2 oW 111.0 oW 110.8 oW
West Transect
East Transect
19.0 oN
18.8 oN
18.6 oN
111.2 oW 111.0 oW 110.8 oW
19.0 oN
18.8 oN
18.6 oN
111.2 oW 111.0 oW 110.8 oW
West Transect
East Transect
Isla de Socorro Island Mass EffectIndices
PO
4 in
shor
e
Flu
or in
shor
e
Chl
-a in
shor
e
Zoo
Den
Zoo
Div
Gel
Den
Mne
k D
en
PO
4 of
fsho
re
Flo
ur o
ffsho
re
Chl
-a o
ffsho
re
Legend
0.00
0.50
1.00
Socorro_east
0.00
0.50
1.00
Socorro_west
0.0
19.0 oN
18.8 oN
18.6 oN
111.2 oW 111.0 oW 110.8 oW
West Transect
East Transect
19.0 oN
18.8 oN
18.6 oN
111.2 oW 111.0 oW 110.8 oW
19.0 oN
18.8 oN
18.6 oN
111.2 oW 111.0 oW 110.8 oW
West Transect
East Transect
44
Figure 15 a-c. Surface Current vector plot and Temperature, salinity, density and fluorescence cross-section plots for three inshore -to-offshore transects around Isla de Socorro. Location and depth of CTD casts are shown by dashed lines in cross-section plots. Depth scale has been limited to upper 200m to emphasis surface features, though CTD casts frequently reached 1000 meters or more. Data interpolation by VG Gridding in ODV, 350 x-scale and 30 y-scale was used to help elucidate sloping isolines for each parameter. Temperature range 5-20 °C, salinity range 33.2-34.2 psu, density (s -t) 22-27 kg/m3, chlorophyll-a fluorescence 0.0-0.6. a) Surface Current vector plot. Surface current patterns around Isla Socorro are complex and suggest presence of eddies along both transects. However, these features are likely aspects of a regional scale eddy field rather than island-scale processes (recall Figures 7 and 8a-c).
45
b) East Transect. Note change in temperature, salinity and density scales from Catalina and Guadalupe islands. Surface mixed layer is warmer, saltier but also narrower than for other islands. The pycnocline is strongly stratified, but shallower than previously seen around other islands. Is explains low surface fluorescence but a well-developed sub-surface maximum, presumably supported by ‘deep’, nutrient rich waters extending into the euphotic zone.
46
c) West Transect. Strong, but shallow stratification again limits surface fluorescence but supports a developed sub-surface maximum. Given the maximum is skewed toward shore, despite lack of evidence for coastal upwelling, suggests a terrestrial source for this expression of mass effect.
47
Table 6. Summary of shipek grab sediment sampling_ Island Mass Effect study. Phi-scale and sorting index calculations followed Boggs (2001). Digital image analysis of sediment samples using Image J software allowed quantitative assessment of sediment reflectivity which was used to measure terrigenous content. Lower grey value indicates darker sediments, and thus greater terrigenous content. Poor sorting and high terrigenous content of sediment samples suggested a site of terrestrial runoff and thus a source of nutrients supporting island mass effect. ISLAND Location Mean
Sediment Size (phi scale)
Mean Sediment Size
(µm)
Sorting Index
ReflectivityGrey Value
Description Interpretation of Runoff
Catalina East 3.30 125 0.99 moderate
136 Sandy, mostly silty, rounded sediments; no organics
No
North 1.17 500 0.89 moderate
128 mostly silty with some small sand; sediments fairly well rounded but some angular; no organics
Yes *
West 3.77 63 1.00 poor
153 mostly sandy & angular, no organics
No
Guadalupe North 2.30 250 0.91 moderate
94 Fine sand, rounded, no smell, many long worm tubes, small crabs, polychaetes
Yes *
East 1.77 250 1.13 poor
119 granular and sandy, angular, shell fragments and organic "fluff", algal fragments
No **
South 1.77 250 0.95 moderate
122 granular and sandy, angular, no smell, small brittle stars and worm tubes
No
Socorro East 2.77 125 1.29 poor
100 Many small shell fragments and silt, slightly angular, no smell of organics
Yes *
West 0.40 1000 1.63 poor
95 Many large shell fragments, sand, and silt, large size range, both angular and well rounded, no smell
Yes *
* Island transects with terrestrial runoff that also corresponded to regions of significant island mass effect. ** Island transects where absence of terrestrial runoff corresponded to area of significant island mass effect.
Tow area was derived by calculating distance in meters between successive GPS positions (every minute). Net opening was 1.0 m wide by 0.5 m tall with a net mesh of 335 µm. Zooplankton density is recorded as wet volume displacement per tow area (ml/m2). Micronekton (>2cm) and gelatinous zooplankton were removed using a 1 cm mesh sieve and biomass (volume displacement) was determined; data available upon request. Lantern fish (Family Myctophidae), spiny lobster larvae (phyllosoma), eel larvae (leptocephali) and Halobates spp. were sorted from net contents and recorded as numbers caught per tow. Floating plastic and tar was also sorted from net contents, counted and recorded as numbers collected per tow. ND represents stations were no data was collected for that parameter.
50
Table 8. Meter net station data for S213. Station # (S213-)
Date (2007)
Local Time (+8
GMT)
Target Tow Depth
(m)
Zoop Density (ml/m3)
Zoop Diversity
(H')
Mycto #
Phylo #
Lepto #
General Locale Descriptive Significance
006 14-Oct 0949 195 0.255 0.82 0 0 0 Catalina Island Island Mass Effect
010 15-Oct 1820 181 0.089 0.34 1 0 0 Catalina Island Island Mass Effect
013 16-Oct 0225 208 0.206 0.47 0 0 0 Catalina Island Island Mass Effect
Tow area was derived by calculating distance in meters between successive GPS positions (every minute). Net volume based on 1MN = 1 meter diameter frame . Net mesh of 335µm. Micronekton (>2cm) and gelatinous zooplankton were removed using a 1 cm mesh sieve and biomass (volume displacement) was determined; data available upon request. Lantern fish (Family Myctophidae), spiny lobster larvae (phyllosoma) and eel larvae (leptocephali) were sorted from net contents and recorded as numbers caught per tow. All tows were oblique tows, for Island Mass Study tows ranged form 0 to within 50m of the seafloor, while samples for CICMAR target range was 0-250m. ND represents stations were no data was collected for that parameter.
51
Table 9. Tucker trawl station data for S213. Station # (S213-)
Duplicate station numbers indicate multiple net deployments occurring in sequence during the tow. Net1 was open from the surface down to the deepest target depth and represents an oblique tow. This net was frequently combined with Net 3, an oblique tow from depth back to the surface. A trigger weight closes Net 1, opening Net 2; the latter was towed for 30’ at a specific target depth, also corresponding to an ecological zone based on position relative to the oxygen minimum zone (OMZ). Again a trigger weight was used to close Net 2 and open Net 3. Net fra me was 1 m2 and nets were 333 um mesh. Micronekton (>2cm) and gelatinous zooplankton were removed using a 1 cm mesh sieve and biomass (volume displacement) was determined; data available upon request. Lantern fish (Family Myctophidae), spiny lobster larvae (phyllosoma) and eel larvae (leptocephali) were sorted from net contents and recorded as numbers caught per tow. ND represents stations were no data was collected for that parameter.
Jigging occurred with the ship hove to and deck lights on to attract squid. Duration of attracting lights recorded in minutes. Maximum number of squid observed at a single moment during the observation period. However, this does not reflect the variable nature of squid presence. At times, squid were visible near surface during the entire observation period, other times squid were episodically present. Small jigs were 10 cm in length on hand lines, large jigs were 25cm in length on rod and reel. Specimen measurements in cm. ML – mantle length, FW – mantle fin width, LT – long tentacle length, StT – short tentacle length.
54
Figure 16. Oxygen minimum zone (OMZ) upper and lower limits along the Eastern Pacific Ocean (Helly and Levin 2004). Region marked by dashed lines indicates area of S213 cruise track. Enlarged figure (right panel) graphically represents the working hypothesis for the Trophic Dynamics research team (see Table 12). As the upper limit of the OMZ shallowed, so to would the extent of diel vertical migration by zooplankton and myctophids. The coincident accumulation and increased densities of these trophic levels in the upper water column would represent good foraging areas (on a regional/latitudinal scale) along the Baja coast for the jumbo flying squid Dosidicus gigas.
55
Figure 17. Zooplankton and Myctophid distribution in relation to oxygen minimum zone . Center panel: Dissolved oxygen cross-section plot showing the position of the OMZ with location (depth range and latitude) of neuston and Tucker Trawl net tows super-imposed. Three regions are distinguished by depth of the OMZ. Upper panel: Day/night distribution of zooplankton density* by region. Lower panel: Day/night distribution of Myctophid density*.
* Calculation of density was normalized across gear type by transforming neuston net data to tow volume (ml/m3) assuming a net height of 0.25m.
REGION IDay/Night Distribution
0 25 50 75 100
mid OMZ layer
upper OMZ layer
upper watercolumn
surface
DE
PTH
ZO
NE
% Zooplankton Density (ml/m3)
REGION IIDay/Night Distribution
0 25 50 75 100
mid OMZ layer
upper OMZ layer
upper watercolumn
surface
DE
PTH
ZO
NE
% Zooplankton Density (ml/m3)
REGION IIIDay/Night Distribution
0 25 50 75 100
mid OMZ layer
upper OMZ layer
upper watercolumn
surface
DE
PTH
ZO
NE
% Zooplankton Density (ml/m3)
REGION IDay/Night Distribution
0 25 50 75 100
mid OMZ layer
upper OMZ layer
upper watercolumn
surface
DE
PTH
ZO
NE
% Myctophid Density (ml/m3)
REGION IIDay/Night Distribution
0 25 50 75 100
mid OMZ layer
upper OMZ layer
upper watercolumn
surface
DE
PTH
ZO
NE
% Myctophid Density (ml/m3)
REGION IIIDay/Night Distribution
0 25 50 75 100
mid OMZ layer
upper OMZ layer
upper watercolumn
surface
DE
PTH
ZO
NE
% Myctophid Density (ml/m3)
REGION IDay/Night Distribution
0 25 50 75 100
mid OMZ layer
upper OMZ layer
upper watercolumn
surface
DE
PTH
ZO
NE
% Zooplankton Density (ml/m3)
REGION IIDay/Night Distribution
0 25 50 75 100
mid OMZ layer
upper OMZ layer
upper watercolumn
surface
DE
PTH
ZO
NE
% Zooplankton Density (ml/m3)
REGION IIIDay/Night Distribution
0 25 50 75 100
mid OMZ layer
upper OMZ layer
upper watercolumn
surface
DE
PTH
ZO
NE
% Zooplankton Density (ml/m3)
REGION IDay/Night Distribution
0 25 50 75 100
mid OMZ layer
upper OMZ layer
upper watercolumn
surface
DE
PTH
ZO
NE
% Myctophid Density (ml/m3)
REGION IIDay/Night Distribution
0 25 50 75 100
mid OMZ layer
upper OMZ layer
upper watercolumn
surface
DE
PTH
ZO
NE
% Myctophid Density (ml/m3)
REGION IIIDay/Night Distribution
0 25 50 75 100
mid OMZ layer
upper OMZ layer
upper watercolumn
surface
DE
PTH
ZO
NE
% Myctophid Density (ml/m3)
56
Table 11. Shipek grab station data for S213.
Station # (S213-)
Date (2007)
Time (local +8
GMT)
Sample Depth
(m)
Locale Qualitative Description
005 14-Oct 0848 81 Catalina Island
Moderate olive brown, 5 y 4/4, olive gray 5 y 3/2; Sandy, mostly silty, rounded sediments; no organics
007 14-Oct 1134 61 Catalina Island
Grayish olive 10 y 4/2; mostly silty with some small sand; sediments fairly well rounded but some angular; no organics
011 15-Oct 2208 91 Catalina Island
Olive gray 5 Y 3/2, Grayish olive 10 Y 4/2, mostly sandy & angular, no organics
014 16-Oct 0550 101 Catalina Island
Olive gray 5 Y 3/2, silty/clayish & well rounded; Benthic polychaete, tube worms, small annelid, stinky (organic)
026 21-Oct 0930 96 Isla de Guadalupe
Moderate yellowish brown 10 YR 5/4, granular and sandy, angular, no smell, small brittle stars and worm tubes
031 22-Oct 1215 62 Isla de Guadalupe
Light Brown 5 YR 5/6, granular and sandy, angular, shell fragments and organisc "fluff", three different species of brown algae, 1 piece green algae, 2 small pieces of tar
034 23-Oct 0843 113 Isla de Guadalupe
Grayish brown 5 YR 3/2, Moderate brown 5 YR 3/4, small pebbles, sand, silt, mostly very angular, worm tubes, greed seaweed, shell fragments, brittle coral (fan-shaped light pink)
034 23-Oct 0858 79 Isla de Guadalupe
Dusky brown 5 YR 2/2, fine sand, rounded, no smell, many long worm tubes, small crabs, 2 pink worms (3 cm), eye sack
050 29-Oct 2116 12 Bay of Cabo San Lucas
moderate olive brown, 5 y 4/4, olive gray 5 y 3/2; Sandy, mostly silty, rounded sediments; no organics
068 10-Nov 1816 92 Isla Socorro dark yellowish brown, 10YR 42, small shell frags and silt, slightly angular, shell frags but no smell
069 10-Nov 2314 92 Isla Socorro Moderate yellowish brown 10 YR 5/4 (bigger shell frags), and moderate brown, 5YR 3/4 (silty stuff), lots of large shell frags, sand, and silt, large size range, both angular and well rounded, no smell
078 15-Nov 0000 19 Isla la Marieta
Shells and fragments, tube worms, some fragments of seaweed, no smell
Sediment samples (100 ml) were wet sieved and percent wet volume determined, data available upon request.
57
Table 12. Student research topics for S213.
Research Topic I: Regional Comparisons - Physical, Bio-Chemical
Folasade Morvan
Vertical distribution of nutrients and bacteria throughout the O.M.Z.
Ellie Kane, Lucy Rozansky, and Tim Groves
Hydrographic patterns in the Southern California Bight and coastal Baja peninsula in relation to ENSO conditions
Delia Adriana Daza
Geographic patterns of nutrients and heterotrophic bacteria
Research Topic II: Trophic Dynamics
Emily Cira, Rebecca Inver, and Thomas Stout
Zooplankton vertical migration and community parameters across the oxygen minimum zone of the Eastern Pacific
Tasia Blough, and Katie Shaughnessy
Variation of myctophid vertical migration patterns and diet throughout the oxygen minimum zone of the Eastern Pacific
Marjorie Crowley Distribution of larval Dosidicus gigas in the surrounding waters of the Southern California Bight
Adam Smith Zooplankton density and it’s correlation to megafaunal distribution along the S-213 Cruise Track
Research Team III: Island Mass Effect
Shiloh Schlung
The role of terrestrial runoff in island mass effect around three islands in the Eastern Pacific
Isaac Schoepp
The role of wind-driven upwelling in the island mass effect around Santa Catalina, Isla Guadalupe, and Isla Socorro islands
Kristine Unkrich Island eddies at Catalina, Guadalupe, and Socorro: Where are they located and how are they formed?
Aspen Gavenus
Larval nekton distribution and zooplankton density: determining primary mechanisms of island mass effect
58
References Boggs, S., Jr., 2001. Principles of Sedimentology and Stratigraphy, 3rd Ed. Prentice Hall, Upper Saddle River, N.J. Martinez, Elodie and Keitapu Maamaatuaiahutapu, 2004. Island mass effect in the Marquesas Islands: Time variation. Geophysical Research Letters, vol 31, L18307. Messie, M. et al., 2006. Chlorophyll bloom in the western Pacific at the end of the 1997-1998 El Nino: The role of the Kiribati Islands. Geophysical Research Letters, vol 33, L14601. Dandonneau and Charpy 1985. An empirical approach to the island mass effect in the south tropical Pacific based on sea surface chlorophyll concentrations. Deep Sea Research 32(6): 707-721. Hernandez-Leon 1991. Accumulation of mesozooplankton in a wake area as a causative mechanism of the “island mass effect”. Marine Biology 109: 141-147. Helly and Levin 2004. Global distribution of naturally occurring marine hypoxia on continental margins. Deep Sea Research 51: 1159-1168. Wolanski and Hamner 1988. Topographically controlled fronts in the ocean and their biological influence. Science 241: 177-181.