Upwelling. LO: interpret effects of upwelling on production of marine ecosystems. John K. Horne University of Washington

Transcription

1 Upwelling LO: interpret effects of upwelling on production of marine ecosystems John K. Horne University of Washington

2 Effects of Upwelling - Upwelling enhances biological productivity, which feeds fisheries. - Cold upwelled water alters local weather. Weather onshore of regions of upwelling tend to have fog, low stratus clouds, a stable stratified atmosphere, little convection, and little rain. - Spatial variability of transports in the open ocean results in upwelling and downwelling, which results in redistribution of mass in the ocean, which results in wind-driven geostrophic currents through Ekman pumping.

3 Coriolis Force - combined effects of gravity and a rotating planet - due to Eularian reference frame: Eularian - to the right in the northern hemisphere - determined by Rossby number (low R o, high effect) - ratio of centrifugal to Coriolis accelerations Ro = U fl U velocity, f Coriolis parameter ( 2Ωsin(Φ)), L Length scale angular velocity, latitude ocean ~1, atmospheric cell 0.1, playing catch ~6000

4 Ekman Transport - thin (~100 m), wind driven frictional layer at the top of the ocean - transport is at right angles to wind but variation in wind causes convergences and divergences

5 Upwelling Fronts - pycnocline intersects sea surface in upwelling zone during favorable winds - eastern boundary currents, with wind blowing equatorward - inshore cool, dense, nutrient rich waters to euphotic zone to replace Ekman transported surface layer water - winds relax, surface waters shift back inshore, front disappears

6 Coastal Upwelling Locations

7 Micro-Turbulence Enhances Contact Rates Gerritsen & Strickler 1977 Mackenzie & Leggett 1991 Rothschild & Osborn contours show increase in contact rate as a function of u and v - enhances contact rates with prey by order of magnitude

8 Upwelling Examples - Humbolt Current: perfect storm of location (latitude, eastern terminus of equatorial wave guide), upwelling, and ENSO effects - California Current: eastern limb of subtropical gyre in N. Pacific Others: Benguela, Canary Islands, Somali

9 Dominance of Peruvian Anchovy Catch 1970: 1/6 world s catch - MSY did not work over long term - worked as long as good recruitment - feed on plankton - fish biomass supports many predators - used for fish meal - El Nino fish left, bird pops crashed - birds consume 1.5 million tonnes

10 Peruvian Anchovy S-R - catch and effort recorded since start of fishery - Schaefer model assumed - f = total effort (GRT year -1 )

11 Anchovy -- Sardine Cycle Peru - decadal trend in anchovy and sardine landings - El Ninos: 69-70, 72-73, 75-76, 82-83, 86-87,91-92, 94-95, 97-98, 02-03, 06-07, closed fishery in recovered in 1990 s

12 Peru: Anchovy, Hake, Sardine - fish scale accumulation #(1000 cm) -2 y -1 - hake and anchovy in phase, sardine out of phase (?) devries & Pearcy 1982

13 California Current Sea surface temperature Summer flow patterns

14 Anchovy - Sardine Competition? sardine anchovy California Current - sardine largest single species fishery - sardine collapse replaced by anchovy - closed fishery in 1970 Soutar & Isaccs 1974 Did anchovy replace sardine?

15 Sardine Stock-Recruitment some increased survivorship at low stock size Spawning Biomass - fishery reduced spawning stock biomass - anchovy filled the niche Murphy 1966

16 Sardine Recovery California Current - numbers estimated from DEPM methods - stock recovered in 1990 s Deriso et al. 1996

17 Not so Fast Longer Temporal Scale - scales in cores of anaerobic sediments - shows that abundance changed dramatically over 2000 years - collapses and recoveries without fishing pressure - periodicity of 30 to 35 years - similar life histories, competition, reduced predation - fishing enhanced environmental effects to magnify and accelerate collapses - collapses occurred during rapid environmental changes Baumgartner et al. 1992

18 Large-Scale Factors Influencing Annual Sardine Landings Populations? - sardine rise and fall in eastern boundary upwelling regions - sardine anchovy dominance switch observed over time and space - inverted V s getting higher and narrower Bakun 1996

19 Sardine Pacific Synchrony? - Californian and Japanese fisheries in phase 1920 s 1930 s - crashed for 3 decades s recovery + South America - Benguela out of phase - indirect reactions to El Nino and regime shifts Kawasaki 1983

20 Increased Upwelling? Bakun (1990) Hypothesized that global warming, due to CO 2 increases, leads to lower nighttime cooling and increased daytime heating of land, intensifying the pressure gradient between land and sea Result: intensified alongshore winds and upwelling; positive feedback from increased ocean cooling Mote and Mantua (2002) Results from 3 models showed no increased upwelling through the 21 st C

21 Lecture Summary - started with a review of upwelling physics - upwelling as a physical factor influencing growth and survival - examples of sardine and anchovy in Peru and California - combination of biological and physical factors - multiple factors operating over different temporal scales