Production Vs Biomass

OCN 201 Biology Lecture 5

Production vs Biomass

Biomass = amount of carbon per unit area (= standing stock * C/cell)

Units (e.g.): g C m-2

Primary Production = amount of carbon ﬁxed per unit area per unit time

Units(e.g.): g C m-2 yr-1

✴ both also commonly reported per unit volume (m-3) Primary Production Secondary Production - the production of - the production of autotrophic biomass heterotrophic biomass

The production of heterotrophs depends upon the production of autotrophs What controls the production (growth) of autotrophs?

Resource Limits on Primary Productivity

Light

Cell

6CO2 + 6H2O C6H12O6 + 6O2

Nitrate PhosphateNutrients Trace Metals Respiration and Remineralization

Energy Food C, N, P O Heterotrophic 2 CO2 + H2O Respiration & Organism Remineralization NO 3 Growth PO4 Trace Metals

Limits on Primary Production

• Light Energy: amount depends on • Depth • Angle of the sun

• Nutrient Supply: depends on • Import • Recycling Light Decreases with Depth

Depth Effects on PP Photosynthesis or Respiration low high 0 Declines with Depth

50 Depth (m) Relatively Constant with Depth 100 Depth (m) 100 50 0 Depth (m) low 100 Photosynthesis 50 or Respiration 0 low Now add mixing... Photosynthesis or Respiration Compensation Depth Net Productivity Gross Productivity high high availability oflight mixing controls photosynthesizing phytoplankton are mixing respiring

euphotic zone Base of Sverdrup’s critical depth theory (1953) intended to explain the timing of the spring bloom in the North Atlantic

Mesoscale features also affect mixing, and nutrient and light availability

(e.g., Mahadevan et al. 2012. Science)

Key Concepts

Primary productivity by phytoplankton is restricted to the surface ocean (that’s where the light is)

The euphotic zone refers to the zone above the compensation depth. Anywhere above that depth, photosynthesis exceeds respiration Typically - this occurs at ~1% light levels Key Concepts

• Gross primary production: total organic material produced by autotrophs • Net primary production: production remaining after subtracting respiratory needs of the autotrophs • Compensation depth: depth at which gross primary production rate = respiration rate (Net productivity = 0)

Light Intensity Varies with Angle of the Sun

• Solar angle varies daily, seasonally and with latitude • Lower angles = lower energy density = more energy dissipated by atmosphere = less productivity Sun Angle and Energy

Noon

Morning or Atmosphere Afternoon

Earth

Sun Angle and Energy

Summer

Winter Sun Angle and Energy

Tropical

Polar Ocean Color

Limits on Primary Productivity

Light Energy Cell

6CO2 + 6H2O C6H12O6 + 6O2

Nutrients Nutrient Limitation

• With sufﬁcient light, growth will continue until nutrients run out • Limiting nutrient: the nutrient that runs out ﬁrst

Exponential Growth

Time Cells Amount

Time

Cells

Phosphate Amount

Limiting Nutrient Nitrate Time (Organic N & P)

NO3 PO4 (Inorganic) Euphotic Zone Deeper Ocean Fecal Pellets Dead Animals Marine Snow

NO3 PO4 Decompose

Nutrient Concentration

0 5 10 15 20 25 30 0 Nutrients depleted 500 in euphotic zone 1000 1500 Nutrients enriched 2000 in deep water 2500

Depth (m) 3000 3500 4000 • Most biomass in the sea is in the upper 200 meters • Nutrients become depleted in most surface waters because of primary production Concentration Biomass

Depth (m) Dissolved Nutrients

Recycle (decompose) NO3 PO4 (Inorganic) Euphotic Zone Mixing Deeper Ocean and Fecal Pellets Dead Animals Upwelling Marine Snow

NO3 PO4 Decompose Modes of Production

• Regenerated Production: productivity based on nutrients that are recycled within the euphotic zone • New Production: productivity based on nutrients imported (mixed or upwelled) into the euphotic zone

Source of New Production

• Mixing by storms, high winds - Strong density stratiﬁcation inhibits mixing - Stratiﬁcation greatest in the tropics • Upwelling (coastal or equatorial) Equatorial Upwelling

Equatorial Upwelling Coastal Upwelling

Coastal Upwelling Key Concepts

• Nutrients are stripped from surface waters by photosynthesis and lost to deep water • Areas with upwelling or deep mixing by storms are very productive because nutrients are returned to the surface • Areas with little mixing or upwelling become nutrient limited and have low productivity EVEN IF THERE IS LOTS OF LIGHT

Patterns of Productivity Seasonal Productivity

Tropical (Upwelling)

Seasonal productivity Poles

Polar productivity latitude

Temperate productivity light light nutrients

Tropics Tropical productivity Winter Spring Summer Autumn Winter

(schematic after Lalli & Parsons Fig 3.9) Productivity Patterns

• Tropics (except equator): Lots of sunlight, but low nutrients due to strong thermal stratiﬁcation = persistently low productivity • Equatorial upwelling: strong upwelling and lots of sunlight = persistently high productivity • Temperate: Seasonal deep mixing of nutrients plus moderate sunlight = spring bloom, small fall bloom • Polar: High nutrients, but light limited except during summer = one major summer bloom

Questions?