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.

Oceans in the news: November

Here are a couple of ocean related articles that have been in the news recently!

17th November – ‘Emissions of CO2 driving rapid oceans 'acid trip'’ (BBC, 2013)

This article focuses on ocean acidification and follows suitably on from some of my latest posts. Following the 2012 Third Symposium on the Ocean in a High-CO₂ World, the article discusses the Summary for Policy Makers report that has just been released and that presents a summary of all the ocean acidification research that was raised at the symposium.

The report states that due to anthropogenic emissions of CO₂, the world’s oceans are acidifying at an unprecedented rate and this is happening quicker than at any point in the past 300 million years. Unsurprisingly, this has had many implications on marine life, including a 30% species loss in some ocean ecosystems. Furthermore, it has been proposed that by 2100, acidification could increase by 170%.

I would definitely advise giving the article a quick read over as it provides a good introduction to some of the main points in the report and to ocean acidification in general. If you have some more time on your hands though, take a glance at the full report here!

21^st November – ‘English seas get new marine conservation zones’ (BBC, 2013)

27 new marine conservation zones (MCZs) will be created around the English coast, in order to protect sea-life from dredging and bottom-trawling.

These are two anthropogenic fishing methods detrimental to ocean habitats and ecosystem health. Bottom-trawling is an extremely invasive method and consists of a net that is dragged across the ocean floor, often removing corals and sponges with it. Dredging, on the other hand, consists of a rakelike device that scrapes across the ocean bed. Both pose a major threat to any bottom-dwelling organisms and can dramatically alter biological communities. For instance, the disturbance of coral and sponges from bottom-trawlers can destroy many species’ habitats that they use for breeding, shelter and feeding and normally results in reduced population numbers (The Ocean Conservancy, 2002). This is just one example of how these two fishing methods can impact marine ecosystems; there are many, many more.

Amongst those species protected by this governmental scheme are seahorses, coral reefs and oyster beds. Even though it is a step in the right direction towards protecting these species from anthropogenic fishing activities, the number of MCZs proposed is nowhere near the 127 recommended by scientists for an ‘ecological coherent’ network. Hopefully more can be done in the next three years where there are plans to designate two more phases of MCZs.  

25^th November – ‘New widget counts global warming happening at 4 Hiroshima atomic bombs per second’

This is a really cool new widget that tries to put global warming into terms that the general public can more easily visualize. Its aimed to try and debunk the myth that global warming has stopped or paused. Now I know it is not directly ocean related, but the changes we are seeing in our seas are all related to global warming! Check it out!

Deadly Threat No. 3: Ocean deoxygenation

Principally, seawater’s oxygen concentration is determined by both the diffusion of atmospheric oxygen across the air-sea interface and the consumption through microbial respiration (Falkowski et al., 2011). The resultant oxygen concentration naturally varies with time and space, but in no way accounts for the decline in oxygen content that we are seeing today. Referred to as ocean deoxygenation, it is the third ‘deadly’ threat that the ocean faces and comes in two forms.

The first form of oxygen depletion, occurring in the central North Pacific Ocean and tropical oceans, relates to the impacts of global warming and regional freshening. In both of these open basins, observations over the past 50 years have shown falling oxygen levels (Keeling et al., 2010). Behind this decline are a number of factors connected to climate change (Bijma et al., 2013), such as:

1. The decreased solubility of oxygen in a warming ocean.
2. The increase in respiration rates with rising ocean temperatures.
3. The reduced ventilation in high-latitude areas linked to increased ocean stratification. The latter inhibits the exchange of oxygen between surface and subsurface waters, ultimately reducing the supply of oxygen to the ocean’s interior (Keeling et al., 2010).

Currently, though, it remains uncertain as to whether this deoxygenation in the open ocean is a long-term trend related to climate change (the factors listed above), the outcome of natural cyclical processes, or a combination of both (Bijma et al., 2013).

Elsewhere, on the western coast of North America, anoxic (lacking oxygen) waters have been found on the inner shelf, adjacent to the upwelling zone. These continental margin upwelling systems are naturally prone to deoxygenation, due both to the low oxygen source waters and the high flux of nutrients that promote high phytoplankton biomass that then settles to the seabed where it is decomposed by respiring bacteria. However, for the western coast of North America, it was discovered that the upwelling of oxygen depleted waters was due to an increase in the frequency and strength of upwelling inducing winds; events symptomatic of climate change (Chan et al., 2008).

The second form of oxygen depletion refers to the rapid rise in coastal hypoxia from anthropogenic eutrophication. This results from nutrients found in agricultural fertilisers and sewage pollution that find their way into the ocean through urban runoff, causing blooms of algae and plankton (Bijma et al.,2013). Eventually these die and fall to the seabed, where they are decomposed by oxygen consuming bacteria. This lowers the oxygen content of the water, depleting the supply available for marine life. It is for this reason that these hypoxic areas have become known as marine dead zones – there is simply not enough dissolved oxygen to support marine life. Since the introduction of industrially produced nitrogen fertiliser in the late 1940s, oxygen depleted zones have spread, but with a lag of 10 years between their use and the incidence of hypoxia. Indeed, over the past 50 years, the number of dead zones has approximately doubled each decade (Diaz and Rosenberg, 2008). This correlates to human’s continued settlement in coastal regions.

Figure 1 shows the location of the ocean's dead zones. Those areas most affected include the Baltic Sea, which harbours seven of the world’s 10 largest marine dead zones, and also the northern Gulf of Mexico (National Geographic, 2013).   Inland seas and estuaries are also extremely prone to coastal hypoxia; some examples include the Kattegat, the Black Sea and Chesapeake Bay (IPSO, 2013).

Figure 1. Map of aquatic dead zones around the world (NASA, 2010). Click here to see the high-resolution version.

However, it is important to note that the research into ocean deoxygenation is still in its infancy. Prior to 1960, it is extremely rare to find accurate measurements of oceanic oxygen concentrations, making it hard to accurately discern patterns (Falkowski et al., 2011). Large gaps in data also make it difficult to make reliable predictions for the future. Keeling et al. have predicted that by 2100, the ocean’s oxygen content will have declined by between 1 and 7% - notice the uncertainty (2010). This will undoubtedly have profound consequences on the ocean’s biology, but also its biogeochemical cycling. This post has ended up rather long though, so I shall save these for next time!

The biological implications of ocean acidification

A couple of posts ago, I explored the chemistry behind ocean acidification but did not touch on any of the implications on marine life. Hence, I will be covering this today, focusing mainly on calcification rates and acidosis. If you missed my explanation of ocean acidification, you can find it here.

Firstly, marine calcifiers such as reef-forming corals, protozoans, molluscs, crustaceans, echinoderms and some algae are greatly affected by the decrease in carbonate ions (CO_­3^2-) associated with CO₂ dissolution (Bijma et al., 2013). They use CO₃^2- to build and maintain their calcium carbonate shells and skeletons, but this becomes increasingly difficult with falling CO₃^2- concentrations. Consequently, many calcifiers have shown reduced rates of calcification in response to the increasing partial pressure of CO₂ (Fabry et al., 2008).

For tropical reef-building corals, it is predicted that calcification rates will have reduced by 20-60% once CO₂ concentrations reach double that of preindustrial levels. A change of this magnitude could slow growth rates, making reefs much more vulnerable to erosion. Furthermore, with the associated reductions in CO₃^2- ions, it is likely that much weaker skeletons will form and thus, allow erosional processes to occur at quicker rates than previously (Guinotte and Fabry, 2008). A report issued on Friday, following last year’s Third Symposium on the Ocean in a High-CO₂ World, delivers some extremely worrying facts. They state with high confidence that ‘If CO₂ emissions continue on the current trajectory, coral reef erosion is likely to outpace reef building sometime this century’. Take ocean warming into account and the prospect is even more dire – erosion could potentially outpace growth by mid-century, once CO₂ levels reach 560 ppm. If this happens, there would be consequences for coral biodiversity, with many species losing their habitat (IGBP et al., 2013).

Coral reef near Fiji

However, it is not all doom and gloom for tropical corals. Fine and Tchernov found that two species of scleractinian corals were able to survive under acidic conditions (pH values of 7.3-7.6) (2007). Initially, their skeletons dissolved leaving the coral polyps exposed, but when pH returned back to normal, the polyps were able to recalcify with no lasting effects. This offers a glimmer of hope for corals’ future in a high CO₂ world. Still, we have to remain cautious as the study did not consider the effects of predation on the naked polyps and there has been discrepancy about its representativeness (Guinotte and Fabry, 2008).

As for cold-water corals, 70% will experience unsaturated waters by 2100 (high confidence), with this beginning as early as 2020 for some (IGBP et al., 2013). As highly productive ecosystems with a rich biodiversity, this would impact the many deep-water organisms that rely on them as feeding grounds, habitat and nursery areas (Guinotte and Fabry, 2008).

Many plankton and zooplankton species are also affected by changes to the carbonate chemistry of the ocean (see Figure 1). This is potentially detrimental considering they form integral components of the marine food chain. Amongst those most sensitive to ocean acidification are pteropods – the major planktonic producers of aragonite. In waters that are unsaturated with respect to aragonite, it has been observed that pteropods are unable to maintain their shells and consequently, have begun dissolving (Orr et al., 2005). This is occurring in the Southern Ocean today, impacting predators such as pink salmon (IGBP et al., 2013). The future for pteropods that are endemic to polar regions depends on their ability to transition to lower latitudes, where warmer, carbonate-rich waters await (Orr et al., 2005).

Figure 1. Photos showing scanning electron microscopy photographs of the coccolithophorid Gephyrocapsa oceanica under different carbon dioxide concentrations; normal in the top image (300 ppm) and elevated in the bottom (780-850 ppm). The distinct structural malformations can be clearly seen under higher carbon dioxide concentrations (Riebesell et al., 2000). 

However, once again, it is not all bad. Whilst the majority of marine calcifiers do see decreasing calcification rates under acidic waters, some organisms actually benefit; these include some fleshy algae, seagrasses and phytoplankton groups (although further research is still required to fully understand the underlying mechanisms) (IGBP et al., 2013). It appears that under higher CO₂ concentrations, these experience increased photosynthesis and, therefore, growth (Gattuso and Hansson, 2011).

Lastly, for many marine animals, including invertebrates and some fish, the acidification of ocean waters can result in acidosis. This is where high environmental CO₂ levels cause an increase in carbonic acid in the bloodstream. Consequently, the blood's pH is lowered, affecting many cellular processes. Acidosis can lead to metabolic and behavioural depression, lowered resistance and asphyxiation (Howard et al., 2012). Compared to less mobile organisms, fish appear to be more resistant to ocean acidification as they do not have extensive calcium carbonate shells (IGBP et al., 2013). However, particularly in larval fish, acidic seawater has led to impaired sensory performance, altered behaviour and decreased growth rates, all of which impact predator-prey relationships (Howard et al., 2012). Overall though, this area remains insufficiently explored and further research is required to fully understand the physiological mechanisms behind individual animal responses to elevated CO₂ levels.

To round things up, whilst a few organisms can tolerate or actually benefit from acidic waters, many respond negatively to ocean acidification. Survival, growth, abundance and larval development for many organisms is reduced, alongside their ability to form and maintain shells and skeletons. These impacts have repercussions on marine food webs and biodiversity, which, in turn, ultimately affects society. It has been suggested that over generations, acclimatization and evolutionary adaption may occur that mitigates or even compensates for ocean acidification. To support this, there are a few examples of limited adaption from the paleo-record, but knowledge in this area remains patchy, not helped by the fact that every species differs in its potential to adapt (Wittmann and Pörtner, 2013). What is most problematic, however, is that the rate of ocean acidification today is unprecedented; 30-100 times faster than at any point in the recent geological past (Bijma et al., 2013). It is, therefore, hard to imagine how marine life could possibly ever adapt quick enough to these rapid changes in ocean chemistry.

Coastlines in an ice-free world

Yesterday, I was pointed to some fascinating maps created by National Geographic that depict the world’s new coastlines if all the ice on earth (five million cubic miles) were to melt. The scenario sees sea levels rise by 216 feet, causing drastic changes to Earth’s shorelines. The maps show both the present-day and new shorelines, as well as providing an informative timeline of ice history and it’s distribution on Earth. Click here to see the maps.

From the depicted rise in sea level, Europe sees some of the biggest changes; the Netherlands disappear and so too does the majority of Denmark. Eastern England, western France and northern Italy also suffer submergence. Those cities lost to the ocean include London, Venice, Stockholm and Amsterdam. 

Map of Europe following a 216 foot sea level rise (National Geographic, 2013)

Cross the Atlantic Ocean, over to North America, and the entire Atlantic seaboard is engulfed, losing cities such as New York, Norfolk and Charleston. The Gulf coast and Florida also disappear, meaning Houston, New Orleans and Miami are no more. Moving down to South America, two huge new Atlantic inlets are formed from the Amazon and Paraguay river basins.

Over in Asia, much of China, India and Bangladesh are flooded, again saying goodbye to large cities such as Shanghai, Dhaka and Hong Kong.

Australia is also heavily impacted. Much of its coastal strip has been lost to the rising ocean, proving catastrophic for the 80% of Australians living in this region. Additionally, a new sea has formed in the centre of the continent. 

As for Antarctica, it is virtually unrecognisable - not surprising considering the East-Antarctica ice sheet alone contains four-fifths of Earth's ice. 

Map of Antarctica following a 216 foot sea level rise (National Geographic, 2013)

Of all the continents, Africa is least affected. However, the increase in temperature due to the continual carbon emissions has made Africa less inhabitable by this stage. 

According to National Geographic, the time taken to reach this ice-free planet will ‘probably’ exceed 5,000 years, although ‘no one really knows’. If it does happen, however, it will be the first time that Earth has been ice-free in more than 30 million years. 

The maps are interesting to look at and do help increase the public’s awareness of future sea level rise; however, they have received criticism based on their scientific grounds (Bump, 2013). For one, people have questioned where they have ‘plucked’ 216 feet from, having been unable to find this figure anywhere else. Resultantly, in comparison to other studies, it has been suggested that National Geographic have underestimated this figure. However, the U.S. Geological Survey have concluded this argument, stating that the most recent data projects a sea level rise of 206 feet; thus National Geographic have slightly overestimated. More importantly though, the quoted rise in sea level has not taken into account the thermal expansion of water that occurs under rising ocean temperatures (I mentioned thermal expansion in one of my earlier posts, 'Deadly Threat No. 1: It's getting hot in here'). This will contribute ‘between 0.20-0.63m per °C of global mean temperature increase’ (IPCC, 2013). Thus, with rising global temperatures, 217 feet is a vast underestimate for future sea level rise and this has to be kept in mind when viewing the maps.