It is therefore extremely concerning that reefs are in the worst state they have ever been in. The programme was not exaggerating how serious this is. No reef anywhere on Earth is what it was 20 years ago, and is barely recognisable from 100 years ago. One important consideration in ecological science is setting a baseline – a ‘pristine’ environment, or a ‘fully grown’ fish – to act as a control with which to assess the extent of change. This is usually a nearby area, or the same location a few months or years before. What is problematic is that these baselines change generation to generation (2).

As a young person, the places I have dived and snorkelled that I consider ‘amazing’ would be considered degraded to senior divers who started diving 50 years ago. On a fieldcourse in Bermuda this summer I was struck by the beauty of an offshore reef we visited to measure coral cover – I was surprised to hear the scientists working at BIOS considered this site degraded. The same issue occurs with fisheries, where what is considered a ‘big fish’ by one generation would have been considered a juvenile by a great grandparent. The programme’s spectacular footage from French Polynesia represents the kind of community that most coral reefs would have possessed at one time – today represented by very few extremely remote places. It is thought that before human interference, apex predators like groupers and sharks would have made up the majority of biomass in a reef community (3). Perspective is powerful, and as scientists we must select ours carefully.

Additionally, the corals on which the entire reef ecosystem depends are imperilled worldwide. The largest living structure on Earth, the Great Barrier Reef, bleached two consecutive years in 2016 and 2017 – the first time this has ever happened – in the worst bleaching event in its history. Corals in the Caribbean have declined by 40% in the last five decades (4). Something that I have found as fascinating as shocking considering contemporary life on Earth in the context of its entire history. This decline is a geologically significant event – such large formations dying en mass in a blink of an eye in terms of Earth history is an unusual freak event. The science is increasingly showing that humans are the most influential species of vertebrate in the history of life on Earth.

There have been encouraging suggestions of long-term adaptability – some of the research coming from the Coral Reef Lab at NOC. Some reefs in the Middle East have showed less extreme responses to bleaching. However, I attended a seminar by Dr. Leonard Nurse of University of the West Indies in Barbados a few weeks ago, who is involved in Caribbean coastal management and the Intergovernmental Panel on Climate Change. He made no qualms about mentioning that “no evidence exists that corals can adapt to unabated thermal stress over decadal timescales”.

Change is occurring at both regional and global scales, and although reefs are already declining globally, regional management, intergovernmental climate change agreements and robust science are key to boosting reef longevity and resilience. Seeing the enormous engagement and widespread reaction to the Blue Planet episode is extremely encouraging, and I look forward to seeing a new generation inspired to understand and protect these beautiful habitats.

1. Pascal, N. et al. Economic valuation of coral reef ecosystem service of coastal protection: A pragmatic approach. Ecosyst. Serv. 21, 72–80 (2016).
2. Roberts, C. The Unnatural History of the Sea. (Island Press/Shearwater Books, 2008).
3. Friedlander, A. M. & DeMartini, E. E. Contrasts in density, size, and biomass of reef fishes between the northwestern and the main Hawaiian islands: the effects of fishing down apex predators. Marine Ecology Progress Series 230, 253–264 (2002).
4. Gardner, T. A., Côté, I. M., Gill, J. A., Grant, A. & Watkinson, A. R. Long-Term Region-Wide Declines in Caribbean Corals. Science (80-. ). 301, 958–960 (2003).

The post Blue Planet | Episode 3 | Coral Reefs appeared first on Exploring our Oceans .

It has been a very interesting week 2 on the MOOC, and we have seen a lot of debate about tidal power, and how structures like the Severn Barrage would affect the estuary and wildlife, versus the potential “green power” benefits.

It has also been quite a different week with the content, a little bit of maths, congratulations to everyone who gave it a go, and don’t forget you can download the PDF with the answers from FutureLearn.

One of the most commonly asked questions has been about the circulation system, and what would happen if a large volume of freshwater was introduced to the system. This is a particularly fascinating area of oceanography, and the subject of continued debate. Fortunately, we do have some answers, and as this forms a significant part of my PhD, I thought I would try to explain what we know about this phenomena, and what happened the last time, some 8200 years ago.

After the end of the last ice age, much of what is now North America was covered in a large ice sheet: the Laurentide Ice Sheet (LIS). This ice sheet was between 2400m-3000m high at is thickest point, comparable to Greenland today. When the planet started to warm, this ice began to melt, and the process took several thousand years to complete. This is an image from the excellent book by William Ruddiman, many of these images can be found here. 

When ice sheets melt, they often form what are known as Pro-glacial lakes, large bodies of cold, fresh water surrounding the edge of the ice. This is normally a result of the land rebounding once the weight of ice is removed (much like a cushion you have been sat on, the indent remains for some time, but it slowly returns to a neutral level, this is called isostatic rebound). The sediments pushed forwards by, and deposited at the front edge of the ice sheet form moraines, large mounds that often dam the water behind them. There are many such lakes in existence today, though none of the same size as that which surround the LIS. This lake is known as Lake Agassiz.

This lake suffered a catastrophic outburst at around 8.47 thousand years before now, and as a result, a large volume of freshwater entered the North Atlantic, by some calculations this happened in less than a year. This has the effect of reducing sea surface salinity and temperature in one of the most crucial regions of the world for deepwater formation. This outburst is believed to be the cause of a slow-down in the strength of the Thermohaline Circulation System that you have been reading about this week.

Over the next 300 years, there is a near global signature of change. Over Greenland, it was between 5.7-11 degrees celcius cooler, and most of this change happened in less than a decade. The monsoonal regions of the world show a near contemporaneous decrease in the strength of the monsoon, and rainfall patterns changed substantially over much of Europe. In addition, rapid sea level rise occurred, though there are widely varying estimates of this, the most commonly reported figures are between 1.2-2m of sea level rise.

This is not the only time that this type of event has occurred. Around 12.7 thousand years ago, when the LIS was still a significant size, an outburst cause more significant cooling, and for those still following, there are older events known as “Heinrich Events” where armadas of icebergs entered the North Atlantic following rapid deglaciation. I won’t go into details here, but here is a good link.

 Here is a more technical overview from NASA

A summary from the IPCC report on rapid climate change 

Feel free to ask questions!

Millie

@GeoMillie

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