New Zealand’s changing oceans

Figure 1: Difference in daily mean air temperature at 2 m (left) and Sea Surface Temperature (right) compared to the climatological values within the New Zealand environs derived from the Hau Moana and Moana Ocean Hindcast, respectively. Both variables are directly connected by air-sea exchange and show a similar warming trend along the last 30 years.    

In recent discussions at the 28th meeting of the Conference of the Parties to the United Nations Framework Convention on Climate Change, or COP28, the urgency of acting on Earth’s rising temperatures was highlighted.

COP28 emphasized the role of the ocean as a carbon and heat sink, and the necessity to improve our understanding and monitoring. Despite the scientific consensus on human-induced global warming, regional impacts and variability are still difficult to determine. In part, this is related to the reliance on satellite observations for most of our ocean monitoring.

However, these satellite observations only observe the surface, while subsurface temperatures, particularly in coastal areas, are still largely under-observed. While approximately 90% of the excess heat available in the atmosphere is absorbed by the oceans, because of the sparsity of observations at depth the amount of energy that is transferred to the ocean interior is poorly understood. 

The effects of global warming on altering the deeper open ocean circulation patterns—which may have enduring effects on Earth's climate—have received a lot of attention lately. With less observational data available within Exclusive Economic Zones (EEZ), understanding the impact of warming oceans on local economics, food security and the blue economy is poorly understood. 

The Moana Project has demonstrated that most of the warming occurs in waters down to 1000 metres around New Zealand. Significant ramifications result from this: on a local level, it affects the fishing industry and causes localised marine heat waves (MHW) that can decimate marine habitats; on a global level, it affects the deep circulation

We have demonstrated that intense and long-lasting MHW events are directly influenced by subsurface warming. These MHWs have direct impacts on the ocean ecosystems, including mortality of sea sponges and kelp forests and bleaching of coral reefs, and have been associated with economic losses for the fishing and aquaculture industries in New Zealand. 

Successful attribution studies in our region require extensive and accurate observations, such as the ones provided by the Moana Project Mangōpare sensors. The integration of such a system into numerical models through data assimilation provides a powerful tool better understand, monitor and predict our oceans. 

Presently New Zealand leads the world through the observing and modelling capacity developed during the Moana Project. The challenge now is in how we ensure the continuation of this system, setting an example for the international community and working towards a sustainable and responsible use of our ocean resources. 

Dr. Brett Beamsley & Dr. Joao De Souza

Figure 2: Daily mean Ocean Heat Content change in New Zealand waters in relation to the long-term mean, as revealed by the Moana Ocean Hindcast. While the warming trend is evident, it is not uniformly distributed throughout the water column.