Saturday, 23 February, 2019

Study Reveals the Ocean Will Shift Color This Century

The more phytoplankton in the water the less blue the seas appear scientists say The more phytoplankton in the water the less blue the seas appear scientists say
Theresa Hayes | 05 February, 2019, 14:24

Satellites should detect these changes in hue, providing early warning of wide-scale changes to marine ecosystems.

The molecules in water absorb all but the blue part of the spectrum of sunlight, and the water reflects that blue color back.

The ocean's colors could change as the climate warms, though it won't be very noticeable to the naked eye.

Hickman said: "Crudely speaking, where the water is now quite blue because the phytoplankton [have a] relatively low biomass, you are going to see the water getting more blue, and where the ocean is relatively more green because the biomass is higher, you are going to see [it] getting [greener]". As a result, the simulation could show changes to the light being absorbed and reflected to the ocean based on the presence of phytoplankton. This can then provide a more accurate reflection of the climate trend than calculating chlorophyll levels from this data, which only gives a sense of the amount of phytoplankton.

Mayotte, an archipelago in the Indian Ocean.

Ocean color changes depending on how sunlight interacts with what's in the water.

"Colour is going to be one of the early signals", said Stephanie Dutkiewicz, a principal research scientist in MIT's Centre for Global Change Science and a co-author of Monday's study in Nature Communications.

"The nice thing about this model is, we can use it as a laboratory, a place where we can experiment, to see how our planet is going to change", Dutkiewicz says. They also "fix" nitrogen (convert Nitrogen from the air into compounds), making them an important part in the enrichment of oceanic waters.

Scientists have been measuring the color of the world's oceans since the late 1990s, using these measurements to determine chlorophyll levels and as such, those of phytoplankton.

As the agency explains, "productivity is expected to drop because as the surface waters warm, the water column becomes increasingly stratified; there is less vertical mixing to recycle nutrients from deep waters back to the surface".

The numbers of phytoplankton present in oceans is crucial.

In the interim, Dutkiewicz said, paying close attention to changes in the oceans' colour can offer the first clues of the changes that are underway.

Areas that are already quite blue, especially subtropical areas (such as those between the Tropic of Cancer and Tropic of Capricorn) will become even bluer, according to the study. Whereas water around the poles could be set to get even greener.

When the group compared results of their model to actual measurements of reflected light that satellites had taken in the past, they found the two agreed well enough that the model could be used to predict the ocean's color as environmental conditions change in the future.

This will drive a colour change in more than 50 percent of the world's seas by 2100.

For years, the government has maintained satellites that monitor the kind of light, or radiance, that is coming from the Earth's surface.

For Mr. Strutton, "What this study has shown is that although the greenness of the oceans, the amount of chlorophyll might only be changing by small amounts, what's important is that the type of phytoplankton might be changing more dramatically".

"The satellites are going to be the sentinels", she said. "Different types of phytoplankton absorb light differently, and if climate change shifts one community of phytoplankton to another, that will also change the types of food webs they can support".

Rarotonga, in the Pacific Ocean.

A new study from researchers at the Massachusetts Institute of Technology finds that more than half of the world's oceans will shift color by the year 2100, due to changes in the types and location of phytoplankton.