Although the ocean occupies more area than the land, land-based species are impacting the ocean in untold ways. Dr Anjani Ganase looks at some findings from current research in ocean science.

Deep ocean impacts from hurricanes

Scientists from New Zealand discovered that some cyclones in the Pacific Ocean may leave behind a biological marker in the ocean that is stored in the sediments. Scientists observed a large phytoplankton (micro-organisms living suspended in the water) bloom after Cyclone Oma off the coast of Vanuatu.

Cyclones form as the ocean surface heats up. The cyclone cools any area in its path by churning up the water and at times even drawing cold and nutrient-rich waters up from the deep.

The phytoplankton take the opportunity to feed on the nutrients and multiply. In nearshore environments, cyclones ejected large amounts of water over land masses, resulting in significant run-off of land-based nutrient that results in algal blooms in the surrounding water. This had never been observed offshore in the middle of the ocean. Using satellite imagery capable of detecting chlorophyll (a pigment that absorbs sunlight), scientists were able to track a sizeable phytoplankton bloom two weeks after cyclone Oma, which was a category one storm that moved at a relatively slow pace.

So what happens to the plankton biomass after blooming?

While some of the plankton will serve to feed marine life, a large portion of the plankton will sink to the bottom of the ocean. Coring the sediment at the site revealed that such a bloom event at the scale of the tropical cyclone Oma is incredibly rare.

However, other storms have been shown to produce other bloom events in the South Pacific (14 observations for the area). The intensity of the bloom depends on the size of the storm and the speed of movement.

With respect to climate change, as oceans heat up, we expect more severe cyclone events to churn up and drive more phytoplankton blooms in the ocean.

Researchers are uncertain of the positives and negatives of this.

Loss of oxygen on coral reefs

Researchers collaborating across several universities found that hypoxia (limited availability of oxygen) on coral reefs was more prevalent than previously thought.

The scientists monitored 32 reefs across 12 locations including Japan, Panama, Hawaii and Taiwan. They put out oxygen sensors and other probes to track the variability in oxygen levels on the reefs during the day and night.

Researchers found the oxygen dropped to the lowest levels in the early mornings (after night-time respiration and absorption of oxygen by marine organisms on the reef). The highest levels were found in the afternoon, with a build-up of oxygen in the water column because of photosynthesis by coral and algae during the day.

Shockingly, they found that up to 84 per cent of the reefs observed may have suffered weak to moderate exposure to hypoxia at some point.

Considering the warming ocean conditions, where warmer waters absorb less oxygen, there is conce