Large scale structures and case studies part 2

Upwelling

Movement of water from deep, underlying masses to the surface

What is an upwelling result from what?

The divergence of surface waters from the coast or other water masses

Upwelling features

-Cold

-Nutrient rich

What is the amount of fish production of one upwelling?

44,700 mg C m^-2y^-1

-Most productive of all marine environments

What is the stereotype of upwellings

-Short food chains

-High transfer efficiency

-Well matched

-High f-ratio

-Oversimplified

Equatorial upwellings

Winds drive rotational currents in the surface ocean, anticlockwise in the north, clockwise in the south, both heading inwards

-When they meet, these pulls surface water apart, drawing water from below

Despite equatorial pacific upwelling having rich NO₃- water what does it have low of?

Chlorophyll a

-High Nitrate Low Chlorophyll (HNLC)

What is expected from eqatorial pacific upwelling?

-Low PP

-Phytoplankton cells < 2 nanometres

-Phytoplankton (cyanobacteria & picoeukaryotes)

-Grazing dominated by microzooplankton

-Phytoplankton too small for mesozooplankton

-Low f-ratio

Where is Galapogas Plume situated?

Equatorial Pacific

Galapogas Plume features

-High chlorophyll a

-Volcanic rock below ocean & volcanic dust from land

-Fertilise water with Fe

When does coastal upwellings occur?

Longshore equatorward winds, offshore currents drag up deep, nutrient rich water to surface

Causes for upwelling

Variability in weather

Example of upwelling affected by different sources of variability in weather:

Arabian Sea

-Seasonal → Monsoon winds

Peru

-El Nino

Benguela

-Frequent changes wind stress

What was the focus of ARABESQUE Cruise

August-September cruise leads to waning of Southwest monsoon

(ARABESQUE Cruise) Upwelling Region features

-Diatoms: Porosira sp (large)

-High phytoplankton biomass

-Large mesozooplankton population

-Low microzooplankton biomass

-Characterisitcs upwelling system

(ARABESQUE Cruise) Offshore Region features

-Phytoplankton: Synechoccocus

-HNAN dominated by zooplankton

-Low mesozzoplankton

-Characteristics oceanic system

El Nino/La Nina (ENSO)

-Easterly winds drive warm surface waters to the west

-Water level ‘piles up’ on the west

-Wind structures can change resulting in the potential energy in this pile being released and flowing back to East (El Nino)

-Major weather and biological impacts

Benguela current (Benguela Upwelling Zone:Case Study 3)

-Massively productive upwelling region

-Variable system based on weather changes supported by Ekman transport

Why is Benguela important? (Benguela Upwelling Zone:Case Study 3)

Supports a commercially important demersal & pelagic fishery

-Anchovy & Pilchard

Benguela features (Benguela Upwelling Zone:Case Study 3)

-Strongly influenced by physical environment

-Upwelling contains South-eastern stress, austral summer

-Tongues cold upwelled water move offshore and northwards

-Mix with warm aged upwelled or oceanic water

What did Painting et al (1993) investigated

Investigated changes in planktonic food web structures by following plume of upwelled water

What did Painting et al (1993) ecounter in his investigation?

3 distinct water masses

-Age identified from temperature & NO₃- data

What were the 3 distinct water masses Painting et al, (1993) found?

-Initial Maturing Upwelled Water

-Intermediate Maturing Upwelled Water

=Aged Maturing Upwelled Water

Initial Maturing Upwelled Water features

-Cold & high NO₃-

-High chlorophyll a and PP

-Diatoms dominated phytoplankton (Skeletonema)

-High bacterial biomass

-Classical food chain

Intermediate Maturing Upwelled water features

-Higher temperature

Low NO₃-

-Lower PP & chlorophyll a

-Diatoms → Nanoflagellates

-Highest bacterial biomass

Aged Maturing Upwelled Water features

-Higher temperatures

-Lower NO₃-

-Low chlorophyll a and PP

-Nanoflagellates

-Lowest bacterial biomass

-Microbial food web

What did Probyn (1985) investigate

This study examines nitrogen uptake by different size-fractionated phytoplankton populations in the southern Benguela upwelling system. Researchers investigated how oceanic, continental shelf, and inshore waters influence nitrogen assimilation across various phytoplankton size classes

What were the key findings of Probyn (1985)

Size-Based Nitrogen Uptake

-Microplankton (>10 µm) showed higher nitrate uptake, dominating nitrogen assimilation in shelf waters.

-Nanoplankton (<10 µm) relied more on ammonium and urea, particularly in oceanic regions.

Environmental Influence

-Upwelling zones provided high nitrate concentrations, supporting larger phytoplankton.

-More stable offshore waters favored nanoplankton dominance, with regenerated nitrogen sources playing a key role.

Nitrogen Cycling & Ecosystem Impact

-The study highlights how different phytoplankton groups contribute to nitrogen cycling, shaping primary production.

-Understanding these dynamics is crucial for predicting ecosystem responses to environmental changes.

What were the F-ratios recorded for diatom bloom and annual average by Probyn, 1985?

Diatom bloom=0.7

Annual average=0.2-0.3

What is the least productive upwelling system?

Benguela

-Upwelling pulses are episodic which equals to mismatch

What wasthe recent increase in Benguela upwelling system?

Increase mesozooplankton due to favourable wind stress

-Mesozooplankton increased 100 fold over 50 years