Scientists Discover Sea Levels Rose in Sharp Bursts During Last Warming
Scientists from Rice University and Texas A&M University-Corpus Christi's Harte Research Institute for Gulf of Mexico Studies have discovered that Earth's sea level did not rise steadily but rather in sharp, punctuated bursts when the planet's glaciers melted during the period of global warming at the close of the last ice age. The researchers found fossil evidence in drowned reefs offshore Texas that showed sea level rose in several bursts ranging in length from a few decades to one century.
The findings appeared Wednesday in Nature Communications.
"What these fossil reefs show is that the last time Earth warmed like it is today, sea level did not rise steadily," said Rice marine geologist André Droxler, a study co-author. "Instead, sea level rose quite fast, paused, and then shot up again in another burst and so on."
André Droxler (seated) and Pankaj Khanna aboard the Schmidt Ocean Institute's research vessel Falkor in 2012. Mark Schrope / Schmidt Ocean Institute
"This has profound implications for the future study of sea-level rise," he said.
Because scientists did not previously have specific evidence of punctuated decade-scale sea-level rise, they had little choice but to present the risks of sea-level rise in a linear, per-year format, Droxler said. For example, the International Panel on Climate Change, the authoritative scientific source about the impacts of human-induced climate change, "had to simply take the projected rise for a century, divide by 100 and say, 'We expect sea level to rise this much per year,'" he said.
"Our results offer evidence that sea level may not rise in an orderly, linear fashion," said Rice coastal geologist and study co-author Jeff Nittrouer.
Given that more than half a billion people live within a few meters of modern sea level, he said punctuated sea-level rise poses a particular risk to those communities that are not prepared for future inundation.
"We have observed sea level rise steadily in contemporary time," Nittrouer said. "However, our findings show that sea-level rise could be considerably faster than anything yet observed, and because of this situation, coastal communities need to be prepared for potential inundation."
The study's evidence came from a 2012 cruise by the Schmidt Ocean Institute's research vessel Falkor. During the cruise, Droxler, study lead author and Rice graduate student Pankaj Khanna and Harte Research Institute colleagues John Tunnell Jr. and Thomas Shirley used the Falkor's multibeam echo sounder to map 10 fossil reef sites offshore Texas. The echo sounder is a state-of-the-art sonar that produces high-resolution 3-D images of the seafloor.
The Schmidt Ocean Institute's research vessel Falkor mapped 10 fossil reef sites offshore Texas with the latest generation of multibeam echo sounder, a state-of-the-art sonar that produces high-resolution 3-D images of the seafloor. Schmidt Ocean Institute
The fossil reefs lie 30-50 miles offshore Corpus Christi beneath about 195 feet of water. Sunlight does not reach them at that depth, but because corals live in symbiosis with algae, they need sunlight to live and only grow at or very near sea level. Based on previous studies of the Texas coastline during the last ice age as well as the dates of fossils samples collected from the reefs in previous expeditions, the Rice team surmised that the reefs began forming about 19,000 years ago when melting ice caps and glaciers were causing sea level to rise across the globe.
"The coral reefs' evolution and demise have been preserved," Khanna said. "Their history is written in their morphology—the shapes and forms in which they grew. And the high-resolution 3-D imaging system on the R/V Falkor allowed us to observe those forms in extraordinary detail for the first time."
A high-resolution 3-D map of Southern Bank off the South Texas coast clearly reveals terraces, which are a characteristic coral reef response to rising sea level. P. Khanna / Rice University
All the sites in the study had reefs with terraces. Khanna said the stair-like terraces are typical of coral reef structures and are signatures of rising seas. For example, as a reef is growing at the ocean's surface, it can build up only so fast. If sea level rises too fast, it will drown the reef in place, but if the rate is slightly slower, the reef can adopt a strategy called backstepping. When a reef backsteps, the ocean-facing side of the reef breaks up incoming waves just enough to allow the reef to build up a vertical step.
A 3-D representation of Dream Bank, a long-dead reef offshore South Texas. The vertical scale of the image has been increased to clearly illustrate the terrace structures that form due to rising sea levels via a process known as backstepping.P. Khanna / Rice University
"In our case, each of these steps reveals how the reef adapted to a sudden, punctuated burst of sea-level rise," Khanna said. "The terraces behind each step are the parts of the reef that grew and filled in during the pauses between bursts."
Some sites had as many as six terraces. The researchers said it's important to note that even though the sites in the study are as much as 75 miles apart, the depth of the terraces lined up at each site. Droxler and Nittrouer credited the find to Khanna's determination. Analysis of the data from the mapping mission took more than a year, and the time needed to respond to questions that arose during the publication's peer-review process was even longer.
"That's the way science works," Droxler said. "This is the first evidence ever offered for sea-level rise on a time scale ranging from decades to one century, and our colleagues expected ironclad evidence to back that claim."
Nittrouer said the scenario of punctuated sea-level rise is one that many scientists had previously suspected.
"Scientists have talked about the possibility that continental ice could recede rapidly," he said. "The idea is that sudden changes could arise when threshold conditions are met—for example, a tipping point arises whereby a large amount of ice is released suddenly into global oceans. When melted, this adds water volume and raises global sea level."
Khanna said it's likely that additional fossil evidence of punctuated sea-level rise will be found in the rock record at sites around the globe.
"Based on what we've found, it is possible that sea-level rise over decadal time scales will be a key storyline in future climate predictions," he said.
The research was supported by Rice University, the Harte Research Institute at Texas A&M University-Corpus Christi and the Schmidt Ocean Institute.
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By James Shulmeister
Climate Explained is a collaboration between The Conversation, Stuff and the New Zealand Science Media Centre to answer your questions about climate change.
If you have a question you'd like an expert to answer, please send it to firstname.lastname@example.org
What was the climate and sea level like at times in Earth’s history when carbon dioxide in the atmosphere was at 400ppm?<p>The last time global carbon dioxide levels were consistently at or above 400 parts per million (ppm) was around <a href="https://www.nature.com/articles/nature14145" target="_blank">four million years ago</a> during a geological period known as the <a href="http://www.geologypage.com/2014/05/pliocene-epoch.html" target="_blank">Pliocene Era</a> (between 5.3 million and 2.6 million years ago). The world was about 3℃ warmer and sea levels were higher than today.</p><p>We know how much carbon dioxide the atmosphere contained in the past by studying ice cores from Greenland and Antarctica. As compacted snow gradually changes to ice, it traps air in bubbles that contain <a href="https://www.cambridge.org/core/journals/annals-of-glaciology/article/enclosure-of-air-during-metamorphosis-of-dry-firn-to-ice/09D9C60A8DA412D16645E6E6ABC1892F" target="_blank">samples of the atmosphere at the time</a>. We can sample ice cores to reconstruct past concentrations of carbon dioxide, but this record only takes us back about a million years.</p><p>Beyond a million years, we don't have any direct measurements of the composition of ancient atmospheres, but we can use several methods to estimate past levels of carbon dioxide. One method uses the relationship between plant pores, known as stomata, that regulate gas exchange in and out of the plant. The density of these stomata is <a href="https://journals.sagepub.com/doi/abs/10.1177/095968369200200109" target="_blank">related to atmospheric carbon dioxide</a>, and fossil plants are a good indicator of concentrations in the past.</p><p>Another technique is to examine sediment cores from the ocean floor. The sediments build up year after year as the bodies and shells of dead plankton and other organisms rain down on the seafloor. We can use isotopes (chemically identical atoms that differ only in atomic weight) of boron taken from the shells of the dead plankton to reconstruct changes in the acidity of seawater. From this we can work out the level of carbon dioxide in the ocean.</p><p>The data from four-million-year-old sediments suggest that <a href="https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2010PA002055" target="_blank">carbon dioxide was at 400ppm back then</a>.</p>
Sea Levels and Changes in Antarctica<p>During colder periods in Earth's history, ice caps and glaciers grow and sea levels drop. In the recent geological past, during the most recent ice age about 20,000 years ago, sea levels were at least <a href="https://science.sciencemag.org/content/292/5517/679.abstract" target="_blank">120 meters lower</a> than they are today.</p><p><span></span>Sea-level changes are calculated from changes in isotopes of oxygen in the shells of marine organisms. For the Pliocene Era, <a href="https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2004PA001071" target="_blank">research</a> shows the sea-level change between cooler and warmer periods was around 30-40 meters and sea level was higher than today. Also during the Pliocene, we know the West Antarctic Ice Sheet was <a href="https://www.nature.com/articles/nature07867" target="_blank">significantly smaller</a> and global average temperatures were about 3℃ warmer than today. Summer temperatures in high northern latitudes were up to 14℃ warmer.</p><p>This may seem like a lot but modern observations show strong <a href="https://journals.ametsoc.org/jcli/article/23/14/3888/32547" target="_blank">polar amplification</a> of warming: a 1℃ increase at the equator may raise temperatures at the poles by 6-7℃. It is one of the reasons why Arctic sea ice is disappearing.</p>
Impacts in New Zealand and Australia<p>In the Australian region, there was no Great Barrier Reef, but there may have been <a href="https://link.springer.com/content/pdf/10.1007/BF02537376.pdf" target="_blank">smaller reefs along the northeast coast of Australia</a>. For New Zealand, the partial melting of the West Antarctic Ice Sheet is probably the most critical point.</p><p>One of the key features of New Zealand's current climate is that Antarctica is cut off from global circulation during the winter because of the big <a href="https://www.tandfonline.com/doi/abs/10.3402/tellusa.v54i5.12161" target="_blank">temperature contrast</a> between Antarctica and the Southern Ocean. When it comes back into circulation in springtime, New Zealand gets strong storms. Stormier winters and significantly warmer summers were likely in the mid-Pliocene because of a weaker polar vortex and a warmer Antarctica.</p><p>It will take more than a few years or decades of carbon dioxide concentrations at 400ppm to trigger a significant shrinking of the West Antarctic Ice Sheet. But recent studies show that <a href="http://nora.nerc.ac.uk/id/eprint/521027/" target="_blank">West Antarctica is already melting</a>.</p><p>Sea-level rise from a partial melting of West Antarctica could easily exceed a meter or more by 2100. In fact, if the whole of the West Antarctic melted it could <a href="http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.695.7239&rep=rep1&type=pdf" target="_blank">raise sea levels by about 3.5 meters</a>. Even smaller increases raise the risk of <a href="https://www.pce.parliament.nz/publications/preparing-new-zealand-for-rising-seas-certainty-and-uncertainty" target="_blank">flooding in low-lying cities</a> including Auckland, Christchurch and Wellington.</p>
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Investment in U.S. offshore wind projects are set to hit $78 billion (€69 billion) this decade, in contrast with an estimated $82 billion for U.S. offshore oil and gasoline projects, Wood Mackenzie data shows. This would be a remarkable feat only four years after the first offshore wind plant — the 30 megawatt (MW) Block Island Wind Farm off the coast of Rhode Island — started operating in U.S. waters.
Corporates Shift<p>Helping to drive offshore growth, U.S. corporate buyers <a href="https://www.dw.com/en/cities-leading-the-transition-to-renewables/a-42850621" target="_blank">are increasingly relying on wind energy to power their businesses</a>. Walmart and AT&T are the two top corporate wind buyers, while 14 newcomers entered the wind market in 2019, including Estée Lauder and McDonald's.</p><p>"Oil and gas companies have jumped into the U.S. offshore wind market, where they can transfer expertise in offshore fossil fuel development to clean energy investments," says Max Cohen, principal analyst, Americas Power & Renewable research at Wood Mackenzie. Many international oil and gas companies have already recognized this huge potential and entered the US offshore wind market, including Orsted, Equinor and Shell.</p><p>"Given the recent tumult in oil prices, fossil fuel companies may more and more be looking to diversify their portfolios, particularly with assets that are contracted or offer returns uncorrelated with oil and gas," Cohen says. "Offshore wind is an area where they may have a comparative advantage, and they can then leverage the experience with that technology to make the leap to onshore wind, solar, and other renewable technologies," he says.</p>
East Coast leads the way<p>"There is enormous opportunity, especially off the East Coast, for wind. I am very bullish," said former Interior Secretary Ryan Zinke. "Market excitement is moving towards offshore wind. I haven't seen this kind of enthusiasm from industry since the Bakken shale boom," he said.</p><p>Offshore wind initiatives require excessive upfront spending: a 250 MW venture costs about $1 billion, based on International Energy Agency data, but as costs fall the tipping point after which costs fall faster gets nearer</p><p>"The opportunity has been created by Northeastern states seeing the large price declines for offshore wind in Europe," says Cohen. Onshore wind is historically the lowest cost renewable resource, but is at its most expensive in the Northeast, he adds. "But costs are falling slower than for other technologies," he says.</p>
Jobs and Coastal Revitalization<p>U.S. wind energy now supports 120,000 US jobs and 530 domestic factories. A study by the University of Delaware predicted that the supply chain needed to build offshore turbines to feed power to seven East Coast states by 2030 would generate nearly $70 billion in economic activity and at least 40,000 full-time jobs. An American Wind Energy Association's (AWEA's) March 2020 report estimated that developing 30,000 MW of offshore wind along the East Coast could support up to 83,000 jobs and $25 billion in annual economic output by 2030.</p><p>Having said that, not all of the jobs are American jobs. The offshore wind developers with commercial leases in the US are all foreign companies. There is growing interest from the shipbuilding sector in the Gulf of Mexico in partnering with offshore wind companies to provide services. As a result, some of the US oil trade associations have submitted comments supporting certain aspects of offshore wind. "However, it is unclear to what extent offshore wind developers plan to use US vessels and crew, and the existing projects did not incorporate US vessels or labor at all," Hawkins says.</p>
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The human body comprises around 60% water.
It's commonly recommended that you drink eight 8-ounce (237-mL) glasses of water per day (the 8×8 rule).
1. Helps Maximize Physical Performance<p>If you don't stay hydrated, your physical performance can suffer.</p><p>This is particularly important during intense exercise or high heat.</p><p>Dehydration can have <a href="https://www.healthline.com/health/how-to-tell-if-youre-dehydrated" target="_blank">a noticeable effect</a> if you lose as little as 2% of your body's water content. However, it isn't uncommon for athletes to lose as much as 6–10% of their water weight via sweat.</p><p>This can lead to altered body temperature control, reduced motivation, and increased fatigue. It can also make exercise feel much more difficult, both physically and mentally.</p><p>Optimal hydration has been shown to prevent this from happening, and it may even reduce the <a href="https://www.healthline.com/health/oxidative-stress" target="_blank">oxidative stress</a> that occurs during high intensity exercise. This isn't surprising when you consider that muscle is about 80% water.<a href="https://pubmed.ncbi.nlm.nih.gov/19344695" target="_blank"><span></span></a></p><p>If you exercise intensely and tend to sweat, staying hydrated can help you perform at your absolute best.</p><p><strong>Summary</strong></p><p><strong></strong>Losing as little as 2% of your body's water content can significantly impair your physical performance.</p>
2. Significantly Affects Energy Levels and Brain Function<p>Your brain is strongly influenced by your hydration status.</p><p>Studies show that even mild dehydration, such as the loss of 1–3% of body weight, can impair many aspects of brain function.</p><p>In a study in young women, researchers found that fluid loss of 1.4% after exercise impaired both mood and concentration. It also increased the frequency of headaches.</p><p>Many members of this same research team conducted a similar study in young men. They found that fluid loss of 1.6% was detrimental to working memory and increased feelings of anxiety and fatigue.<a href="https://www.cambridge.org/core/journals/british-journal-of-nutrition/article/mild-dehydration-impairs-cognitive-performance-and-mood-of-men/3388AB36B8DF73E844C9AD19271A75BF/core-reader" target="_blank"></a></p><p>A fluid loss of 1–3% equals about 1.5–4.5 pounds (0.5–2 kg) of body weight loss for a person weighing 150 pounds (68 kg). This can easily occur through normal daily activities, let alone during exercise or high heat.</p><p>Many other studies, with subjects ranging from <a href="https://www.healthline.com/health/parenting/signs-of-dehydration-in-toddlers" target="_blank">children</a> to <a href="https://www.healthline.com/health/symptoms-of-dehydration-in-elderly" target="_blank">older adults</a>, have shown that mild dehydration can impair mood, memory, and brain performance.</p><p><strong>Summary</strong></p><p><strong></strong>Mild dehydration (fluid loss of 1–3%) can impair energy levels, impair mood, and lead to major reductions in memory and brain performance.</p>
3. May Help Prevent and Treat Headaches<p>Dehydration can trigger <a href="https://www.healthline.com/health/dehydration-headache" target="_blank">headaches</a> and migraine in some individuals.<span></span></p><p>Research has shown that a headache is one of the most common symptoms of dehydration. For example, a study in 393 people found that 40% of the participants experienced a headache as a result of dehydration.</p><p>What's more, some studies have shown that drinking water can help relieve headaches in those who experience frequent headaches.</p><p>A study in 102 men found that drinking an additional 50.7 ounces (1.5 liters) of water per day resulted in significant improvements on the Migraine-Specific Quality of Life scale, a scoring system for <a href="https://www.healthline.com/health/migraine-symptoms" target="_blank">migraine symptoms</a>.<a href="https://academic.oup.com/fampra/article/29/4/370/492787" target="_blank"></a></p><p>Plus, 47% of the men who drank more water reported headache improvement, while only 25% of the men in the control group reported this effect.<a href="https://academic.oup.com/fampra/article/29/4/370/492787" target="_blank"></a></p><p>However, not all studies agree, and researchers have concluded that because of the lack of high quality studies, more research is needed to confirm how increasing hydration may help improve headache symptoms and decrease headache frequency.<a href="https://pubmed.ncbi.nlm.nih.gov/26200171" target="_blank"></a></p><p><strong>Summary</strong></p><p><strong></strong>Drinking water may help reduce headaches and headache symptoms. However, more high quality research is needed to confirm this potential benefit.</p>
4. May Help Relieve Constipation<p><a href="https://www.healthline.com/health/constipation" target="_blank">Constipation</a> is a common problem that's characterized by infrequent bowel movements and difficulty passing stool.</p><p>Increasing fluid intake is often recommended as a part of the treatment protocol, and there's some evidence to back this up.</p><p>Low water consumption appears to be a risk factor for constipation in both younger and older individuals.</p><p>Increasing hydration may help decrease constipation.</p><p><a href="https://www.healthline.com/nutrition/mineral-water-benefits" target="_blank">Mineral water</a> may be a particularly beneficial beverage for those with constipation.</p><p>Studies have shown that mineral water that's rich in magnesium and sodium improves bowel movement frequency and consistency in people with constipation.<a href="http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5334415" target="_blank"></a></p><p><strong>Summary</strong></p><p><strong></strong>Drinking plenty of water may help prevent and relieve constipation, especially in people who generally don't drink enough water.</p>
5. May Help Treat Kidney Stones<p>Urinary stones are painful clumps of mineral crystal that form in the urinary system.</p><p>The most common form is <a href="https://www.healthline.com/health/kidney-stones" target="_blank">kidney stones</a>, which form in the kidneys.</p><p>There's limited evidence that water intake can help prevent recurrence in people who have previously gotten kidney stones.<a href="https://www.cochranelibrary.com/cdsr/doi/10.1002/14651858.CD004292.pub3/full" target="_blank"></a></p><p>Higher fluid intake increases the volume of urine passing through the kidneys. This dilutes the concentration of minerals, so they're less likely to crystallize and form clumps.</p><p>Water may also help prevent the initial formation of stones, but studies are required to confirm this.</p><p><strong>Summary</strong></p><p><strong></strong>Increased water intake appears to decrease the risk of kidney stone formation.</p>
6. Helps Prevent Hangovers<p>A hangover refers to the unpleasant symptoms experienced after drinking <a href="https://www.healthline.com/nutrition/alcohol-good-or-bad" target="_blank">alcohol</a>.</p><p>Alcohol is a diuretic, so it makes you lose more water than you take in. This can lead to dehydration.</p><p>Although dehydration isn't the main cause of hangovers, it can cause symptoms like thirst, fatigue, headache, and dry mouth.</p><p>Good ways <a href="https://www.healthline.com/nutrition/7-ways-to-prevent-a-hangover" target="_blank">to reduce hangovers</a> are to drink a glass of water between drinks and have at least one big glass of water before going to bed.</p><p><strong>Summary</strong></p><p><strong></strong>Hangovers are partly caused by dehydration, and drinking water can help reduce some of the main symptoms of hangovers.</p>
7. Can Aid Weight Loss<p>Drinking plenty of water can help you <a href="https://www.healthline.com/nutrition/how-to-lose-weight-as-fast-as-possible/" target="_blank">lose weight</a>.</p><p>This is because water can increase satiety and boost your metabolic rate.</p><p>Some evidence suggests that increasing water intake can promote weight loss by slightly increasing your metabolism, which can increase the number of calories you burn on a daily basis.</p><p>A 2013 study in 50 young women with overweight demonstrated that drinking an additional 16.9 ounces (500 mL) of water 3 times per day before meals for 8 weeks led to significant reductions in body weight and body fat compared with their pre-study measurements.</p><p>The timing is important too. Drinking water half an hour before meals is the most effective. It can make you feel more full so that you <a href="https://www.healthline.com/nutrition/35-ways-to-cut-calories" target="_blank">eat fewer calories</a>.</p><p>In one study, dieters who drank 16.9 ounces (0.5 liters) of water before meals lost 44% more weight over a period of 12 weeks than dieters who didn't drink water before meals.</p>
The Bottom Line<p>Even mild dehydration can affect you mentally and physically.</p><p>Make sure that you <a href="https://www.healthline.com/nutrition/how-much-water-should-you-drink-per-day" target="_blank">get enough water each day</a>, whether your personal goal is 64 ounces (1.9 liters) or a different amount. It's one of the best things you can do for your overall health.</p>
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