Oceans in the news: December

Here's another post discussing oceans in the news. Unfortunately, there have not been many articles recently, so both of these are early on in December!

4^th December – ‘Experts say the IPCC underestimated future sea level rise’

(The Guardian, 2013)

The article discusses a new study in Quaternary Science Reviews that argues the past IPCC predictions of sea level rise are too conservative. In the paper, the authors conducted a literature survey to find the top 360 sea-level experts before conducting 90 questionnaires. The scientists were asked how large they believed sea level rise would be, under different greenhouse case scenarios, by 2100 and 2300.

In summary:

• The sea-level rise ranges provided by the experts are on average higher than those of the IPCC 5th assessment (see Figure 1).
• For the best case scenario, with strong mitigation, the likely range is 0.4–0.6 m by AD 2100 and 0.6–1.0 m by AD 2300.
•  For the unmitigated warming scenario, the likely ranges are 0.7–1.2 m by AD 2100 and 2–3 m by AD 2300. 

Figure 1. Scenarios of future sea-level rise between 2000-2100 generated from the survey results. Blue represents strong mitigation whilst red denotes the unmitigated scenario. For comparison, the current NOAA sea-level scenarios (dashed lines) and IPCC predictions are shown alongside (vertical bars).

As can be seen, the paper’s predictions are significantly higher than those recently made by IPCC, reflecting the increasing pessimism about future sea level rise. The fact that the scientists in this study were polled individually meant they could express their own opinion and there was no need to come to a consensus position, like that required for the IPCC. Overall, this paper has added fuel to the debate around the IPCC’s conservativeness.

13^th December – ‘EU discards ban will change the way we fish our seas’ 

(The Guardian, 2013)

Article discusses the reforms to the Common Fisheries Policy that have been made in the past week. Most importantly, discards have been banned - the practice of throwing away perfectly good fish due to quotas.

            1 January 2015 – ban on discarding in ‘pelagic’ fisheries takes effect.

            1 January 2016 – ban on discarding in other fisheries.

This will transform anthropogenic fishing practices and help towards more sustainable usage in the future. Furthermore, a legally binding commitment to fishing at sustainable levels has been secured. Scientific advice will underpin all annual quotas, ensuring the health of fish stocks whilst achieving a prosperous fishing industry. This will come into force on 1 January 2014.

Sea creatures? Or plastic?

(Preston, 2012)

After completing my last post on plastic pollution, I found some really clever photographs that I would like to share with you. Taken by the photographer Kim Preston, they show everyday plastic objects floating in the ocean but arranged so they appear like the sea life they are killing. 

(Preston, 2012)

They form part of a series called Plastic Pacific that aims to bring attention to how our disposal of plastic is impacting marine life. In my opinion, it is an extremely clever and effective approach to informing the grossly unaware public about the plastic problem. Their presence is strangely serene and makes the ocean appear lifeless; I just want to dive in and pull them out! 

(Preston, 2012)

The Plastic Sea

I hope you are all having a lovely Christmas Eve spending time with your family or friends. Today's blog post is sort of in the festive spirit, relating to those presents that Santa may, or may not, be bringing you! There is no doubt that over the Christmas period, you will all come into contact with some sort of plastic; whether it be drink bottles, food packaging, a present or some cracker gifts that you have always wanted! The majority of this will be waste (potentially forget your present at this point) and hopefully (!!) you will recycle it. For those of you won't, be prepared to lower your heads in shame.

When plastic is disposed of into a garbage pile, it remains in the environment for years due to its non biodegradable properties. Take, for example, a plastic sandwich bag; this takes approximately 400 years to break down when exposed to air and light (Coral Reef Alliance, 2013). Gradually, the plastic becomes increasingly brittle and breaks into smaller and smaller pieces, ultimately appearing like fine sediment. This is not natural and has many repercussions on the environment, particularly our oceans.

Throughout its decomposition, plastic finds its way into water bodies that then feed in to the ocean. Once there, ocean currents can transport the plastic away and wash it up on shorelines thousands of miles away. A good example of this is The Great Pacific Garbage Patch. This is a region where plastic from all around the world collects due to the Northern Pacific Tropical Gyre. Double the size of the United States, the patch contains an estimated 100 million tons of garbage and reaches to depths of 100 feet below the ocean's surface (Dautel, 2009).  Much of this garbage washes up on the beaches in the area and the video below documents this problem at Midway Atoll, in the Northern Pacific.

This plastic pollution, along with other forms of rubbish, threatens marine wildlife. Sea turtles mistake plastic bags for jellyfish, small fish ingest 'plastic' phytoplankton and this cascades up the food chain to the seabirds that prey on larger fish. On Midway Island, 

'at least 267 different species are known to have suffered from ingesting or becoming entangled in marine plastic debris, including 86 percent of all sea turtles species, 44 percent of all seabirds, and 43 percent of all marine mammals' (Oceana, 2012).

The festive message to take home from this is to please recycle your plastic rubbish (and any other that can be too!) over Christmas and help lessen the anthropogenic impact on our ocean. 

The 'deadly trio' - a triple whammy

Having individually discussed all three consequences of the global carbon perturbation, ocean warming, acidification and deoxygenation, this post will bring everything together and discuss them in terms of the deadly trio. Bijma et al. named them as such because these ‘big three’ have been associated with most of Earth’s five global mass extinctions and, therefore, can easily be considered deadly (2013). This is extremely worrying when you realise that they are all present in our ocean today and are occurring at a much faster rate than has ever occurred in the past 55 million years!

It is this rate that is the critical factor of any carbon perturbation. In the past, carbon perturbations occurred slowly and were sustained over thousands of years, but now, we are releasing the same amount of carbon, just on a much shorter timescale. Resultantly, the Earth system’s capacity to buffer the changes has been exceeded and organisms are now threatened by unprecedented evolutionary pressure (Bijma et al., 2013). As previously discussed, the ocean’s uptake of CO₂ is now outstripping its ability to absorb the carbon - it has exceeded the supply of cations required for the reactions. This decreased buffering capacity has caused a reduction in pH, decreasing the ocean’s saturation state and detrimentally impacting many marine calcifiers (Cai et al.,2011). Simultaneously, the ocean has warmed, which has enhanced stratification and further decreased its ability to absorb CO₂ (Tyrell, 2011). This has lowered the oceans dissolved oxygen content, first due to oxygen’s decreased solubility in warmer waters and secondly, through the reduced ventilation of the ocean interior owing to increased stratification (Keeling et al., 2010). Although I have previously discussed each stressor individually, it is clear they occur simultaneously in the ocean and interact with one another to create synergistic effects.

Together, the deadly trio are not only considerably affecting the productivity and efficiency of our ocean, but are threatening marine life as we know it. Bijma et al. argues that if we do nothing to change the current carbon perturbation, we can expect serious consequences for the marine ecosystem, worse than occurred during the Paleocene-Eocene Thermal Maximum extinction (PETM) (2013). This is the most recent major extinction event that occurred approximately 55 million years ago and is considered to be the closest analogue to current ocean acidification. The current carbon perturbation will undoubtedly continue to have huge implications for the Earth, its ocean and for us, the human population and if we are to do anything to save our ocean from the deadly trio, Gruber argues our starting point is reducing CO₂ emissions (2011).

A breathless ocean

Ordinarily, ocean surface waters have an oxygen concentration of 5-8 ml l^-1. However, as I discussed last time, climate change is altering the ocean’s oxygen content, causing concentrations in some areas to plummet. In regions considered to be under ‘extreme hypoxia’, dissolved oxygen content is less than 2 ml l^-1; a substantial decline from the norm. It is, therefore, hardly surprising that this has drastic consequences for marine life (Bijma et al., 2013).

With oxygen as the principal constraint on growth, declining oxygen levels affect the functioning and growth of many marine organisms (Zimmer, 2010). Many species exhibit stress-related behaviour and for those most vulnerable, such as crabs and starfish (bottom-dwellers), extreme hypoxic conditions can cause widespread mortality (Gewin, 2010).

As deoxygenation has increased, the depth of oxygen minimum zones has shoaled. This has compressed habitats for marine organisms that have a high metabolic rate and oxygen demand. As a consequence, encounter rates between predators and prey have been altered and many species have been forced to migrate in search of oxygenated waters. This has meant we have seen large-scale shifts in the distribution of species (Stramma et al., 2011). However, fishermen in certain regions of the world have learnt to take advantage of this behaviour. Unfortunately for fish, this has meant that even if they manage to swim away and escape the hypoxia, the narrowed water column they can then live in makes them much easier to catch and increasingly vulnerable (Gewin, 2010). Alongside habitat compression, extreme hypoxia also results in a loss of fauna and together, these seriously impact ecosystem energetics and function. This is primarily because microbes decompose the organisms that die, instead of fish predators, and this diverts energy flows away from the higher trophic levels (Diaz and Rosenberg, 2008).

Sustained hypoxic conditions can also affect global biogeochemical cycles. As oxygen concentrations decline, a change in bacteria occurs - from those that require oxygen in order to thrive, to bacteria for whom oxygen is toxic. However, these new bacteria participate in denitrification, which reduces the concentration of nitrate in the ocean and produces nitrous oxide, thereby limiting ocean productivity (CLAMER, 2011). As nitrous oxide is a potent greenhouse gas, ocean deoxygenation could further amplify global warming (Zimmer, 2010).

However, not all species suffer under extreme hypoxic conditions. Humboldt squid are one such example; tolerant of low-oxygen concentrations they feast on the remains of bottom dwellers that have died due to oxygen depletion (Gewin, 2010). Similarly, jellyfish also tolerate lower oxygen concentrations and, consequently, can thrive in hypoxic areas. This is partially because they are able to store reserves of oxygen in their jelly.

Humboldt squid

Overall though, as Diaz and Rosenberg state, ‘there is no other variable of such ecological importance to coastal marine ecosystems that has changed so drastically over such a short time as dissolved oxygen’ (2008: 929).  Ocean deoxygenation is a major global environmental problem today and one that has detrimental consequences for marine life and ecosystems.