marine biogeochemistry

Biogeochemistry in humpback whale feeding and breeding areas

Humpback whales and baleen whales in general form an integral part of Southern Ocean biogeochemistry in a top-down (predation) and bottom-up (nutrient fertilization) forcing of ocean ecosystems (Figure 1). Within this theme, we strive to understand the roles of whales as ecosystem engineers (in the bottom-up rather than top-down forcing of systems) and associated feedback loops within the ocean-atmosphere biogeochemical cycles that may ultimately control whale distribution and movement. Results from this study may allow us to predict whale behavior in future changing climate scenarios.

Figure 1: Whale centric linked ecosystem in the Southern Ocean. For primary production and growth of phytoplankton, macro-nutrients in the region are supplied primarily through ocean circulation whereas micro-nutrients are derived through atmospheric deposition, melting sea-ice or recycled via whale mediation.

For this reason, we need to better understand the phenomenon known as the Southern Ocean paradox – large parts of the Southern Ocean are barren despite having high concentration of macro-nutrients like phosphate, nitrate and silicic acid and thus, are not suitable whale feeding grounds. Research from the past few decades suggests that the productivity in parts of the Southern Ocean is limited because of a lack of micro-nutrients, for example, iron, zinc and other bioactive trace metals that are required for enzymatic functions within phytoplankton cells. 

Despite their importance, measurement of these trace metals in the Southern Ocean are extremely sparse for logistical and technological impediments and a concerted effort is needed to rectify the situation to improve our understanding of biogeochemical pathways and their linkages. For example, research shows that humpback whales are integral in micronutrient re-fertilization in the upper 80 m of the ocean, within what is termed the ‘euphotic zone’, where light drives primary productivity. Whales also act as a slow release source of recycled iron to the upper ocean by feeding on Iron-rich Antarctic krill where the Antarctic krill feed on the phytoplankton that may bloom in regions with high iron.

Little is known if ocean biogeochemistry plays any role in whale migratory routes or where they chose to be for breading. Consideration of spatially large part of Southern Ocean water column  biogeochemistry and associated physical parameters and use of ocean circulation – biogeochemical models may help us understand or predict their transitory and breeding locality.

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Video: CTD Deployment of Plus Penguin from SCALE Project Antarctic.

Main Aims and Objectives

  • Use existing global ocean data products for identifying surface distribution pattern of major nutrients, and where available, micro-nutrients.
  • Use whale hotspot regions as sites to physically measure change in major and micronutrients over a migratory season to understand nutrient cycling and regeneration.
  •  Assess if biogeochemical parameters are driving whale behavior or if whales are responsible for modifying the water column biogeochemistry.

the research runs under 4 major themes