Mary Ann Wilson

Mary Ann Wilson

Mary Ann Wilson

Aug 222014
 
The shell pictured here is a victim of acidification. The normally-protective shell had become so thin and fragile, it is transparent.

The shell pictured here is a victim of acidification. The normally-protective shell had become so thin and fragile, it is transparent.

The significance of our ocean’s impact on greenhouse gas begins with the earliest ocean four billion years ago, when all the atmospheric carbon was absorbed and allowed the earth to cool enough for life to begin. In our modern era, as atmospheric carbon dioxide levels go up, the ocean absorbs more carbon dioxide to stay in balance. Currently the ocean is holding 50 times more carbon than the atmosphere and is slowing the rate of climate change by absorbing about 30 percent of carbon dioxide from cement production and other activities.

But there’s an important side effect. When carbon dioxide reacts with seawater, carbonic acid is formed—the same weak acid found in soda. Carbonic acid releases positively charged hydrogen ions, which lowers the pH level of seawater. Although ocean water is still alkaline, the term “acidification” refers to a gradual shift toward the acidic end of the scale. The pH scale ranges from 0 to 14; 7 is neutral, lower numbers are acidic and higher numbers are alkaline. Over the past 300 million years, ocean pH has averaged about 8.2, but since preindustrial times it has dropped 0.1 to a current average of 8.1. This may not sound like much, but the pH scale is logarithmic, so that a pH of 7 is about ten times more acidic than a pH of 8. Thus, this drop represents a 25-percent increase in acidity over the past two centuries.

Servicing the Santa Monica Bay Observatory mooring’s antenna

Servicing the Santa Monica Bay Observatory mooring’s antenna

There are several reactions that occur between carbon dioxide (CO2), water (H2O), carbonic acid (H2CO3), bicarbonate ion (HCO3-), and carbonate ion (CO32-). But over the long term ocean acidification leads to a decrease in the concentration of carbonate ions in seawater. Together with calcium ions they form the basic building blocks of carbonate skeletons and shells. The decline of carbonate ions impacts the ability of many marine organisms such as corals, marine plankton, and shellfish to build or even maintain their shells.

There are two main forms of calcium carbonate used by marine creatures: calcite and aragonite. Calcite is used by phytoplankton, foraminifera, and coccolithophore algae. Aragonite is used by corals, shellfish, pteropods, and heteropods. When additional calcite and aragonite cannot be dissolved in water, that water is said to be supersaturated; when they can be dissolved, the water is said to be undersaturated for those minerals. Animals that need calcium carbonate are better in supersaturated water as obtaining that mineral from the surrounding water is easier. The saturation of these minerals in seawater decreases with depth, and the transition point between supersaturated and undersaturated conditions is referred to as the saturation horizon. Because aragonite dissolves more easily than calcite, aragonite is the first to be impacted by ocean acidification. For example, one might find the saturation horizon for calcite at 150 meters or even deeper, but for aragonite it would be at 100 meters.

Currently, nearly all of the surface ocean waters are substantially supersaturated with regard to aragonite and calcite. However, more carbon dioxide dissolving in the ocean has caused the saturation horizon for these minerals to shift closer to the surface by 50-200 meters as compared to the 1800s. As the ocean becomes more acidic, the upper shell-friendly layer becomes thinner.

Distribution of the depths of the undersaturated water (aragonite saturation < 1.0; pH < 7.75) on the continental shelf of western North America from Queen Charlotte Sound, Canada, to San Gregorio Baja California Sur, Mexico. On transect line 5, the corrosive water reaches all the way to the surface in the inshore waters near the coast. The black dots represent station locations.

Distribution of the depths of the undersaturated water (aragonite saturation < 1.0; pH < 7.75) on the continental shelf of western North America from Queen Charlotte Sound, Canada, to San Gregorio Baja California Sur, Mexico. On transect line 5, the corrosive water reaches all the way to the surface in the inshore waters near the coast. The black dots represent station locations.

The saturation horizon is much closer to the surface in regions where upwelling occurs, such as along the West Coast from British Columbia to Mexico. That’s because deep water in the North Pacific is naturally rich in CO2, since the deep water has been out of contact with the surface for 1200 to 1500 years. As water travels along the oceanic conveyer belt, it accumulates CO2 through natural respiration processes that break down sinking organic matter, generating CO2 just as humans do when they breathe. Under normal conditions (and even more so under La Niña conditions), winds blow from north to south during spring and summer months along the West Coast creating an effect known as the Ekman Transport, which in turn moves surface water away from the coastline. This warm surface water is then replaced by colder water upwelled from depths between 100 and 300 meters. This deep nutrient-rich water traditionally makes for robust fishery production. However, the naturally highly acidic water is now augmented with man-made carbon dioxide, making this carbon-rich water even more acidic.

In the Northeastern Pacific, corrosive waters are already shoaling into the euphotic zone during upwelling. In 2007 Richard Feely and a team of scientists found undersaturated seawater with respect to aragonite reaching depths of about 40 to 120 meters. In one transect less than 20 miles from shore near the California-Oregon border, the saturation horizon had shoaled all the way to the surface. Without the contribution of anthropogenic CO2, the aragonite saturation horizon would be about 50 meters deeper.

Because of this, the Pacific Northwest oyster-growing industry nearly collapsed before Feely and other scientists were able to help devise strategies and monitoring protocols. In 2007, the Whiskey Creek Shellfish Hatchery in Oregon lost millions of oyster larvae and later discovered that the larvae were being bathed in acidic waters drawn in by intake pipes. Oyster larvae are particularly sensitive in their first few days of life such that carbon dioxide alters shell formation rates, energy usage and, ultimately, their growth and survival. Now, the Whiskey Creek hatchery tries to balance the acidity of its waters by adding soda ash. Costs have increased and production has never fully recovered.

Island Scallops, a shellfish producer in the Georgia Straight near Vancouver, lost all its scallops over a 3-year period from 2010 to 2012, during which time pH levels had dipped to 7.3. CEO Rob Saunders said that this level of pH in the water was something he hadn’t seen in his 35 years of shellfish farming. The loss amounted to 10 million dollars and a third of their workforce (20 people).

No less troubling is the impact of acidification on the food chain. This year, a NOAA-led research team found evidence that acidity off the West Coast has been dissolving the shells of pteropods at double the rate since the pre-industrial era. These tiny free-swimming marine snails make up 45 percent of the diet of pink salmon and are also a food source for herring and mackerel. The highest percentage of sampled pteropods with dissolving shells were found from northern Washington to central California, where 53 percent had severely dissolved shells.

Compared to Southern California, the water north of Point Conception comes from deeper depths up to the surface where the upwelling is stronger and lasts longer—from spring to fall. Because the direction of the coastline changes (from north-south to east-west) south of Point Conception, a weaker upwelling occurs in Southern California from February to May. The same NOAA-led research team found evidence of corrosive waters shoaling to depths of about 20-50 meters in the coastal waters off Washington, Oregon, and northern California; and to depths of about 60-120 meters off southern California.

Anita Leinweber on board the R/V Seaworld.

Anita Leinweber on board the R/V Seaworld.

This has been the pattern for at least the past ten years, according to Dr. Anita Leinweber, a researcher at UCLA who has been measuring acidification levels in Santa Monica Bay for more than a decade. In a 2013 study, Leinweber and co-author Nicolas Gruber published six-year trends for pH and the aragonite saturation state in the Santa Monica Bay from 2003 to 2008. They found that the saturation horizon there reaches 130 meters on average. As the aragonite saturation state changes, this shoaling is exacerbated and the horizon could climb 20 meters by 2050 to reach an average depth of 110 meters.

Median trends for pH are also decreasing by an average of about -0.004 per year between 100 and 250 meters. These trends in Santa Monica Bay are larger in magnitude than most of those reported so far — for example, about -0.003 pH units per year in Monterey Bay. They are also slightly larger than those expected on the basis of the recent trends in atmospheric CO2. The study also noted that the saturation horizon reached its highest point—the top 30 meters—during the height of the upwelling season in April and May. Lower pH and aragonite saturation states were observed during winters when La Niña conditions prevailed, which makes sense given that La Niña conditions intensify upwelling conditions.

At the time of the study’s publication, no statistically significant linear trends had emerged in the upper 100 meters. But this past April, Leinwebier saw a statistically significant trend in surface pH, calculated from additional data which extended to 2013. The pH values in the top meter had been decreasing by about 0.003 per year. (Calculations were not yet complete for other depths.)

Dr. Leinweber and Takeyoshi Nagai attaching water-sampling bottle

Dr. Leinweber and Takeyoshi Nagai attaching water-sampling bottle

“We have evidence already that ocean acidification is happening,” Leinweber said. “It’s not something that we’re making up or something that we know has to come at some point. We actually see it.”

As alluded to above, the effects of ocean acidification will vary with location. For its part, the Catalina Marine Society is acquiring pH and other ocean chemistry data at specific depths near Santa Catalina Island with its depth-profiling program. These data will enable us to determine where the water comes from, where the phytoplankton reside, the acidity of Santa Catalina water, and how much oxygen is available to marine fauna. The goal is to obtain sufficiently dense records to compare to similar data collected in Los Angeles Harbor (by the Southern California Marine Institute), Point Loma (Scripps Institution of Oceanography), Santa Monica Bay, and off the Santa Barbara coast (University of California, Santa Barbara), as well as understand the physical processes operating around the island and develop expectations for what climate change and ocean acidification will bring. The new data will supplement what was previously collected at a single depth (18 m) near Two Harbors, Catalina. Those data, which include pH levels from May 19, 2012 through November 17, 2013, are available to researchers and students at http://www.catalinamarinesociety.org/Scientificmooring.html

Originally published in Catalina Marine Society’s OceanBights, p. 3.

References

Intergovernmental Panel on Climate Change, Climate Change 2013: The Physical Science Basis, Chapter 3, Observation: Ocean

pH Scale, Introduction and Definitions

European Project on Ocean Acidification, FAQs about Ocean Acidification, Ocean carbon chemistry and pH

Skeptical Science, Ocean acidification: global warming’s evil twin

Nicolas Gruber, Claudine Hauri, Zouhair Lachkar, Damian Loher, Thomas L. Frölicher, Gian‐Kasper Plattner; Rapid Progression of Ocean Acidification in the California Current System

NOAA OAR Special Report, Scientific Summary of Ocean Acidification in Washington State Marine Waters

Richard A. Feely, Christopher L. Sabine, J. Martin Hernandez-Ayon, Debby Ianson, Burke Hales; Evidence for upwelling of corrosive “acidified” water onto the Continental Shelf

Kenneth R. Weiss, Los Angeles Times; Oceans’ rising acidity a threat to shellfish — and humans

Brooks Hays, 10 million scallops dead in Canada thanks to overly acidic water

CBC News, Acidic ocean deadly for Vancouver Island scallop industry

N. Bednaršek, R. A. Feely, J. C. P. Reum, B. Peterson, J. Menkel, S. R. Alin and B. Hales; Limacina helicina shell dissolution as an indicator of declining habitat suitability owing to ocean acidification in the California Current Ecosystem

Leinweber and N. Gruber, Variability and trends of ocean acidification in the Southern California Current System: A time series from Santa Monica Bay

Anita Leinweber, Institute of Geophysics and Planetary Physics and Department of Atmospheric and Oceanic Sciences, University of California, Los Angeles, California, interview May 17, 2014.

Catalina Marine Society, Measuring Catalina’s Ocean, Flyer for Boaters

Images:

  1. The shell pictured here is a victim of acidification: NOAA, Ocean Acidification
  2. Servicing the Santa Monica Bay Observatory mooring’s antenna: Anita Leinweber
  3. Distribution of the depths of the undersaturated water: Richard Feeley, Evidence for upwelling of corrosive “acidified” water onto the Continental Shelf
  4. Anita Leinweber on board the R/V Seaworld.: Anita Leinweber
  5. Dr. Leinweber and Takeyoshi Nagai attaching water-sampling bottle
Apr 102014
 

BallonaWetlands The California Department of Fish and Wildlife (CDFW), Santa Monica Bay Restoration Commission, State Coastal Conservancy and the Annenberg Foundation today announced a joint website to provide an initial outline of potential restoration alternatives at Ballona Wetlands Ecological Reserve on the Los Angeles County coast. The website builds on a prior site, and also features scientific studies, history of meetings and information about the wetlands.

The website, ballonarestoration.org, provides an early overview of proposed alternatives that will be presented in a draft Environmental Impact Report/Environmental Impact Statement (EIR/EIS) that is anticipated to be released before the end of 2014. Upon release, interested parties and members of the public will have an opportunity to review and comment on the EIR/EIS.

References

This news release was provided by the California Department of Fish and Wildlife Marine Management News.

Image: Ballona Wetlands Land Trust

 

Feb 182014
 

musselsLittleDume Along every seashore lies an abundance of marine life that has evolved to thrive in two different environments: underwater at high tide and above water at low tide. This unique zone is expected to be strongly influenced by rising air and sea temperatures. In fact, the distribution of intertidal species along the California coast has already shifted in response to climate change. In 1931, a marine biology student named Willis Hewatt screwed bolts onto rocks in the tide pools at Pacific Grove in Monterey Bay, set a line a hundred meters long, and counted every invertebrate creature in 105 square plots. Sixty two years later, graduate students Raphael Sagarin and Sarah Gilman resurveyed 57 of his plots and documented changes in the abundance of 46 of 62 species that were present in the 1930s. Most southern species (10 of 11) increased in abundance, while most northern species (5 of 7) decreased. During this period, shoreline ocean temperature had warmed by 0.790° C, with average summer temperatures up to 1.940° C warmer in the 13 years preceding Sagarin and Gilman’s study than in the 13 years preceding Hewatt’s.

Photograph courtesy Linda Schroeder, Pacific Northwest Shell Club, Seattle, Washington PNWSC.

Photograph courtesy Linda Schroeder, Pacific Northwest Shell Club, Seattle, Washington PNWSC.

In the 1980s, biologists discovered that the Mediterranean mussel (Mytilus gallo-provincialis) had been introduced to Southern California sometime in the last century. Originally from the Mediterranean Sea, the non-native looks so similar to the native Pacific blue mussel (Mytilus trossulus), the two mussels can only be distinguished from each other using genetic tools. Pacific blue mussels, once abundant along much of the coastline, have now been replaced by the Mediterranean mussel all the way from San Diego up to Monterey Bay. The non-native is less successful than the native mussel in colder northern waters, but survives even at warm temperatures that cause heart failure in the native species. To make matters worse, related studies show that predatory snails in Oregon and central California prefer eating the native mussel rather than the invader, most likely facilitating the spread of the invading mussel. It is expected to expand its range at the expense of the native as temperatures increase.

Wesley Dowd

Wesley Dowd

But climate change isn’t just about rising temperatures. Other factors may complicate the picture. Wesley Dowd, a biologist at Loyola Marymount University, noted in a presentation there this past March that besides increased temperature, additional environmental stressors are emerging such as increasing ocean acidification, changing rain patterns leading to diluted salt concentration, rising sea levels and habitat loss. He compared mussels exposed to increased temperatures with and without more food available, and found that having enough food is of equal or greater importance to their survivability. “There’s interaction between these different factors,” he said. “To look at just one thing could result in misleading predictions.”

Besides resorting to migration or just dying out, organisms have two other options. The first is to utilize an existing mechanism to acclimate to new conditions. California mussels (Mytilus californianus) have some potential to respond to rapid weather events. Their membranes can be restructured within hours in response to temperature fluctuations during the tidal cycle, but only when they’re inhabiting high intertidal sites during the summer.

Identifying when organisms will have exhausted their tolerance threshold in response to ocean change could help target the most vulnerable of them for conservation. The cardiac function of the porcelain crab (Petrolisthes cinctipes), for instance, collapses at 31.5° C—very near the maximum temperature it currently experiences in nature (31° C). The survival of these intertidal crabs, which are found above water on the shore and underwater at depths of up to 90 meters from the northern Channel Islands to Alaska, could be threatened by just a slight increase in temperature.

Most cells respond to acute environmental change by inducing a specific set of proteins that function to prevent and repair macromolecular damage. This reaction, termed the cellular stress response (CSR), is key in determining the range of environmental conditions which an organism can endure. Targeting genes involved in the CSR is a relatively new way to define thresholds for physiological function. For example, when mussel body temperatures reach 32° C, often attained on hot days during low tide, genes encoding proteins that repair heat damage in their bodies become active. By 36.5° C, genes are activated to clear cells of proteins that can no longer perform enzymatic activities, leading to a disruption of the organism’s biological rhythms. Researchers Andrew Y. Gracey and Kwasi Connor observed rhythmic or periodic gene expression patterns of mussels, which signified that these animals have a natural rhythm. But when the mussels were heated up to the mid-to-upper 30s C, that natural rhythm became disrupted.

Finally, an organism could respond to shifting environmental conditions over time through genetic change and evolution. That may not happen quickly enough, given that a study in June 2013 suggests species including birds, reptiles, mammals and amphibians need an average of one million years to adapt to a single-degree increase in overall temperature. But Dowd said “the underlying genetic variation upon which physiological variation rests and upon which natural selection might act may rescue populations from the consequences of climate change.”

He and his colleague Mark Denny, a biologist at Stanford University, found that rare heat waves lead to the evolution of a high safety margin in limpets (Lottia gigantea) on the California coast—5 to 7° C above the maximum body temperature they are likely to encounter in an average year. Pointing out that most limpets are unlikely to experience such high temperatures in their lifetimes, Denny and Dowd suggested that the limpets’ generous thermal tolerance is due to the rare thermal events that wipe out the least tolerant individuals, shifting the gene pool towards greater temperature tolerance.

Denny, who is studying next-generation sequencing, is also finding genetic differences between mussels on the sunny and dark side of a rock, where the difference in temperature that two individuals next to each other experience can be up to 15° C. Such genetic variation is the raw material for natural selection. Since mussels mature within a year, a new generation is born every year with the potential for rapid evolution.

“When you put these things together and model how species are going to adapt or evolve in the face of climate change, depending on how much variation exists within the species, you can actually get pretty rapid evolution,” Dowd said. He hopes conservation efforts will focus on preserving enough variation so that there are some genotypes left which can tolerate extreme conditions, and added that it’s not enough to preserve around the mean but to maintain pools of genetic diversity. Perhaps, when further research leads to a more comprehensive understanding of what physiological abilities genes actually control in order to tolerate different conditions, adaption and rapid evolution can be facilitated in species with the greatest genetic variation.

Originally published in Catalina Marine Society’s OceanBights, p. 12

References

Raphael D. Sagarin, James P. Barry, Sarah E. Gilman and Charles H. Baxter; Climate-Related Change in an Intertidal Community over Short and Long Time Scales

George Somero, Caren Braby, Pete Raimondi, Peter Fields; Climate Change and Invasive Species

Dr. Wesley Dowd, Loyola Marymount University, Filtering Environmental Change through the Physiology of Individual Organisms, presented at the Climate Change in Urban Estuaries Symposium on March 25, 2013, Loyola Marymount University

Jonathon H. Stillman, Acclimation Capacity Underlies Susceptibility to Climate Change

Tyler G. Evans, Gretchen E. Hofmann; Defining the limits of physiological plasticity: how gene expression can assess and predict the consequences of ocean change

Kwasi M. Connor, Andrew Y. Gracey; Circadian cycles are the dominant transcriptional rhythm in the intertidal mussel Mytilus californianus

Ignacio Quintero, John J. Wiens; Rates of projected climate change dramatically exceed past rates of climatic niche evolution among vertebrate species

M. W. Denny, W. W. Dowd; Biophysics, environmental stochasticity, and the evolution of thermal safety
margins in intertidal limpets

M. W. Denny, W. W. Dowd, Lisa Bilir, Katharine J. Mach; Spreading the risk: Small-scale body temperature variation among intertidal organisms and its implications for species persistence

Mary Ann Wilson, Predicting Winners and Losers in a Warmer Intertidal Zone

Images:

  1. Mussels: Mary Ann Wilson
  2. Mytilus trossulus to M. galloprovincialis: Linda Schroeder, Pacific Northwest Shell Club, Seattle, Washington PNWSC
  3. Wesley Dowd: Wesley Dowd

 

Jan 092014
 

Over the next century, sea level rise (SLR) in the Los Angeles region may increase 5-24 inches by 2050 and up to 66 inches by 2100. A new study by USC assesses the potential impacts of SLR on the City’s most vulnerable communities and infrastructures in case of a 10-year or 100-year flood under not only current conditions, but in a 0.5 meter and 1.4 meter SLR scenario. Entitled Sea Level Rise Vulnerability Study for the City of Los Angeles, the study was presented Tuesday, January 7, at the Annenberg Community Beach House in Santa Monica. Here are a few highlights of the presentations.

Cars make their way through the flooded north and southbound lanes of 710 Long Beach Freeway, the main artery to Long Beach and Los Angeles ports, on January 19, 2010 in Long Beach, California. A short but forceful storm moved through Southern California producing tornado-like winds in Huntington Beach and floods in Long Beach and San Pedro. (January 18, 2010 - Source: Kevork Djansezian/Getty Images North America)

Cars make their way through the flooded north and southbound lanes of 710 Long Beach Freeway, the main artery to Long Beach and Los Angeles ports, on January 19, 2010 in Long Beach, California. A short but forceful storm moved through Southern California producing tornado-like winds in Huntington Beach and floods in Long Beach and San Pedro. (January 18, 2010 – Source: Kevork Djansezian/Getty Images North America)

Dr. Reinhard Flick, Principal Oceanographer for the TerraCosta Consulting Company, said flooding damage wouldn’t be caused by mean SLR, but by big waves during high tides. Total maximum water level is most damaging and leads to wave damage and coastal erosion. Of major concern is Pacific Coast Highway which cannot be moved.

Brian Holland, Climate Program Director of ICLEI (International Council for Local Environmental Initiatives), said the most vulnerable sectors are waste water and storm water facilities. Because they’re at low elevations, they’re susceptible to inflow from both flood water and ground water. When unsealed sewers get filled up with flood water, they back up and overrun. The same with pump stations – they have to be located at very low elevations because the whole point is to pump water up. If those are impaired, so goes public health and water quality. Similarly, storm water systems are not sized adequately to accommodate the floods of the future, in particular the coastal interceptor sewer which runs along the coast through Venice/LAX sub-area.

Also, ecosystems such as the Bellona Wetlands are highly vulnerable. As sea levels rise, the precarious dynamic of salinity, tidal influence, and the species that live in the wetlands can get off balance quickly. With urban development all around it, the wetlands have nowhere to migrate.

Less vulnerable sectors include potable water, the port and energy facilities. Potable water use pressurized systems so they’re less susceptible to inflow of flood water. The issue is being able to access the pipes during flooding, as well as erosion and the undermining of the structural integrity of the water system. The port is fairly hardened since it’s at a high elevation, so it should be safe in the mid-century time frame. The same goes for energy facilities – in general they’re built at higher elevations. The exception there is the Haynes Generating Station in Long Beach which is a little bit more vulnerable.

Two violent storms in 1983 destroyed over a third of the Santa Monica Pier.

Two violent storms in 1983 destroyed over a third of the Santa Monica Pier.

Parks and open space have fairly low vulnerability, largely because of the adaptive capacity of these systems. They have passive uses, and infiltrates flood water if affected and can rebound quickly. They’re made to withstand weather impacts. The exception are the beaches; in particular Venice, Dockweiler, and Cabrillo Beach, all of which are going to experience more erosion as sea levels rise.

Looking at land use and transportation in San Pedro, Venice and Pacific Palisades, Venice is the most affected. Under the 2100 projections paired with flooding events, high water, and El Nino wave run-ups, Venice will get extensive flooding, so homes, business, transportation infrastructure there will be very vulnerable starting mid-century.

Dr. Dan Wei, Research Assistant Professor in the Price School of Public Policy at USC, said the majority of the damaged buildings will be residential, with wooden structures at most risk.

Dr. Patrick Barnard, a coastal geologist with the USGS Pacific Coastal and Marine Science Center in Santa Cruz, was more concerned about a foreseeable change in wave approach, rather than wave height. Waves coming from the south would mean more damage for southern facing beaches. He was also concerned about salt water intrusion into coastal aquifers.

Hilary Papendick, a Coastal Program Analyst with the California Coastal Commission, said areas that now flood will be permanently inundated, and low lying areas will have water quality problems as water drains back into the ocean as flooding recedes. She said the CCC’s Draft SLR Guidance Document used the best available science, the National Research Council Report’s sea level rise projections for California, as a starting point for looking at SLR. Accordingly, SLR south of Cape Mendocino is rising at a faster rate than the region north of Cape Mendocino, because of the vertical land uplift along much of the Cascadia Subduction Zone. By the year 2100, SLR is projected to increase between 1.5 and 5.5 feet in the area south of Cape Mendocino, and a third of a foot to less than 5 feet north of Cape Mendocino. The exception is Humboldt Bay’s North Spit which “is subsiding and experiencing the highest rate of sea-level rise in the state: a rate of 18.6 inches per century, according to the Sea-Level Rise Science section of the CCC guidance document. The NRC report is also the subject of this blog’s entry, Sea Level Rise in Southern California.

The California Coastal Commission is seeking input on their Draft Sea Level Rise Guidance Document. The deadline for comments has been extended to February 14, 2014. You can submit comments by email to SLRGuidancedocument@coastal.ca.go or mail them to:
SLR Working Group
45 Fremont St.
San Francisco, CA 94105

References

Sea Level Rise Vulnerability Study for the City of Los Angeles

“Sea Level Rise Vulnerability Study for the City of Los Angeles,” Presentation at the Annenberg Community Beach House, Santa Monica, CA; January 7, 2014

National Research Council Report

California Coastal Commission Draft Sea – Level Rise Policy Guidance

Images:

  1. Cars make their way through the flooded north and southbound lanes of 710 Long Beach Freeway: Kevork Djansezian/Getty Images North America
  2. Two violent storms in 1983 destroyed over a third of the Santa Monica Pier; Santa Monica Public Library Image Archives/Paul Silhavy

 

Oct 282013
 

beach-houseWhen this home, and the ones beside it, were originally designed and built, sand buried the entire foundation up to the bottom of the house, and the stairs led right onto the beach. Today, much of the sand is gone, the foundations of the homes are fully exposed and the stairs now lead to an eight-foot drop down to what is at times ocean water instead of beach.

Back in the 70’s, Broad Beach in Malibu used to be about 100-150 feet wide. Since then, the 1.1-mile oceanfront – lined with homes of the rich and famous – has become eroded by winter storms and high tides. When my friend, Devon Low, and I went there this past April, it seemed like it was ready for a name change – maybe something like Slim Sand.

At high tide, waves wash over the bottom steps.

At high tide, waves wash over the bottom steps.

Cliffs and bluffs, the dominant feature of the west coast, have been slowly retreating for thousands of years. Their rate of erosion depends on what they are made of as well as external forces. Cliff and bluff retreat happens periodically and suddenly from a variety of forces. Large blocks fail under heavy rainfall, large waves, or earthquakes. In steep, mountainous areas, failure is often through large landslides or rock falls, usually driven by excess or prolonged rainfall during the winter months. One example is the slide that occurred in November of 2012 when a 600-foot section of Paseo Del Mar in San Pedro below the White Point Nature Preserve suddenly dropped down the cliffside. It was the most damaging landslide on the Palos Verdes Peninsula since the 17th and 18th holes fell to the beach in 1999 from what’s now Trump National Golf Club.

A rising sea level would cause waves to break closer to the coastline and reach the bases of cliffs or bluffs more frequently, thereby increasing the rate of cliff retreat. According to one recent study, a 40” sea-level rise would accelerate erosion rates for southern California by 20 percent. The California Coastal Commission states that for gently sloping beaches, the general rule of thumb is that 50 to 100 feet of beach width is lost for every foot of sea-level rise.

backyard-2 Cliff and bluff erosion is not reversible. The most common response has been to armor the cliff base with rock revetments or seawalls. Ten percent (110 miles) of the California coastline is armored, including 33 percent of the coastline of the four most developed southern California counties: Ventura, Los Angeles, Orange, and San Diego. Despite this protection, coastal storm damage has increased over the past several decades because of intense development and several severe El Niño events. In addition, armored coastline ultimately reduces beach size.

“An armored coast blocks the natural sediment transport from the shore and in California we get a lot of sand on our beaches from creeks,” said Dana Murray, Heal the Bay’s Marine and Coastal Scientist. Thus, beaches cannot migrate landward, and continued flooding of the seaward beach results in a reduction in beach width, and its eventual loss entirely.

This also spells trouble for California grunions, which migrate to Pacific beaches, mostly from Punta Abreojos Mexico, to Santa Barbara, California every spring and summer. “The walls can diminish or even eliminate grunion spawning grounds,” said Melissa Studer, Project Director of the Grunion Greeter Project.

I think I'd be just a bit worried if the foundation of my multi-million dollar beach-front home was as laid bare and undermined as this. Wave action has removed all the supporting sand from around the footing of this home's pier, exposing the wood piling underneath.

I think I’d be just a bit worried if the foundation of my multi-million dollar beach-front home was as laid bare and undermined as this. Wave action has removed all the supporting sand from around the footing of this home’s pier, exposing the wood piling underneath.

“Waves hit the wall and scour the sand out because they don’t have any where else to go, and as they keep hitting the wall, they bring all the sand back out,” Murray said. “So the beach gets eroded more and more. A rock revetment just makes the problem worse. Beach resident may stop it from going further, but in front of it, they’re losing the beach.”

Broad Beach residents want to restore their beach to its original width, and taxed themselves to foot a $20 million plan to borrow 600,000 cubic yards of sand. But these days they’re having trouble finding suppliers. Manhattan Beach has denied them sand from South Bay, so proponents of the privately-funded Broad Beach project are hoping to dredge sand off Dockweiler Beach. However, the Los Angeles County Department of Beaches and Harbors has objected, saying that the Broad Beach project would deplete reserves that might be needed later to replenish other public beaches eroded by rising sea levels.

If sea level increases substantially and wave heights continue to increase, over-topping will become more frequent. “Broad Beach’s rock wall is not supposed to last,” Murray said. “Even in their reports, they say they’ll last no longer than 5 or 10 years anyway because the rocks fall apart.”

In July, Kurt Russell and Goldie Hawn sold their Broad Beach home after two years of trying. Original sticker price: $14.749 million. Final sale price: $9.5 million. A sign of the times.

Originally published in Catalina Marine Society’s OceanBights, p. 12

 

References

California Coastal Commission, Climate Change Impacts on Coastal Erosion and Loss of Sandy Beaches

Tony Barboza, 600-foot section of road quietly slips into ocean

Martha Groves, On Broad Beach, slim progress on restoring sand

Huffington Post, Goldie Hawn, Kurt Russell House Finally Sells In Malibu For $9.5 Million

LA Curbed, 9 Chutzpah-y Things to Know about Hollywood Big Shots’ Plans to Temporarily Fix Shrinking Broad Beach

Melissa Studer, Fish “Walks” on Beach to Spawn

Images:

D. Devon Low

Oct 252013
 

Increased exposure to coastal flooding along the Los Angeles coastline due to sea level rise
Global warming is producing rising sea levels worldwide. But how rapidly is sea level increasing off southern California and how will it affect us? Global sea levels are projected to rise as much as nine inches by 2030, one and a half feet by 2050 and four and a half feet by 2100. Most of this rise is expected to result from the melting of the Greenland and Antarctic Ice Sheets, which store the equivalent of nearly 200 feet of sea level. The onset of deglaciation which began 20,000 years ago slowed to a stop 2000 years ago, then resumed at modern rates sometime between 1840 and 1920. Since 2006, that rate has accelerated.

So far, sea level in Southern California has risen at a slower pace than the global level. However local sea-level increases are expected to surpass the global mean rise, increasing by one foot in 20 years, two feet by 2050 and as much as five and a half feet by the end of the century.

According to a 2012 report by by the National Research Council, that’s because much of California is sinking from the effects of an ice sheet that has long since disappeared. During the last ice age, an ice sheet depressed northernmost Washington, creating uplift around it. Since the ice melted, the flexure in the continental plate began to slowly release, causing uplift in northernmost Washington and subsidence in the rest of Washington, Oregon and California.

For the coast north of Cape Mendocino, tectonics offset that subsidence. Ocean plates are descending below North America at the Cascadia Subduction Zone, causing regional uplift along much of the Washington, Oregon, and northernmost California coast. Global Positioning System (GPS) measurements show this area is rising about 1.5–3.0 mm per year (or 5.9–11.8 inches each century).

However, south of Cape Mendocino in the San Andreas Fault Zone, tectonic plates move horizontally, creating little vertical motion. GPS measurements (which also measure compaction of wetland sediments, and/or fluid withdrawal or recharge), indicate this area is sinking at an average rate of about 1 mm per year (or 3.9 inches each century), though GPS-measured rates vary widely across locations. Records from 12 West Coast tide gauges concur ─ most gauges north of Cape Mendocino show that relative sea level has been falling over the past 6–10 decades, and most of the gauges to the south show that relative sea level has been rising.

Regional sea-level rise also varies due to local factors affecting the dynamic height of the sea, such as wind, air pressure, and surface-heating influence of climate patterns such as the El Niño/La Niña–Southern Oscillation (ENSO) and the Pacific Decadal Oscillation (PDO). These result in changes in ocean circulation on seasonal and multidecadal timescales that involve redistributing mass by altering the temperature and salinity of the upper ocean.

These climate patterns may also explain why California has not yet experienced the same sea-level rise as measured around the globe. Satellite altimetry, tide gauge, and ocean temperature measurements show a long-term increase in sea level off the U.S. west coast. According to Dr. Peter Bromirski’s 2011 study, trends along the West Coast ─ estimated from tide gauge measurements and confirmed by satellite altimetry since 1992 ─ signify relatively flat sea levels since about 1980. The study points to the Pacific Decadal Oscillation (PDO), which alternates between positive and negative phases. Presently in the positive phase, wind-driven ocean currents draw water away from the west coast and pull colder, denser water up from the depths (upwelling), depressing the sea level for the eastern Pacific. If the PDO shifts, as Bromirski suggests it may be doing, the associated wind patterns would shift, reducing upwelling, which could accelerate sea-level rise back to global rates or beyond.

Satellite altimetry records assessed by the Intergovernmental Panel on Climate Change (IPCC) also showed that sea level fell about 0–6 mm each year from 1993 to 2003 along the west coast. The IPCC suggested that the largest fraction of this short-term variation was caused by ENSO. But note that ENSO and the PDO do not act independently of each other. ENSO may play a significant role in decadal and longer sea-level variability. While ENSO can influence the PDO, the PDO can modulate tropical Pacific circulation as well as ENSO.

Higher baseline sea levels could add to storm levels, making extremes more common, leading to more coastal flooding and erosion, inundation, wetland loss, structural damage, and salinity intrusion into coastal aquifers. Add a large El Niño event, and coastal sea levels could rise an additional four to 12 inches for several winter months.

The largest waves have been getting higher and winds have been getting stronger in the northeastern Pacific, according to several observational studies. But wave and wind records go back only about 35 years, and to some extent reflect large El Niños and PDO fluctuations. If proven to be a long-term trend, the frequency and magnitude of extremely high coastal wave events will increase. But if not, sea-level rise will still magnify the impact of storm surges and high waves on the coast. What is currently defined as a 100-year flood today will occur much more frequently as sea level rises and the number of people exposed to risks from 100-year floods will increase substantially. We do have evidence from tidal gauges that tidal ranges are trending up in Southern California, mostly in La Jolla. Coincidentally, the occurrence of high sea level storm extremes has increased at La Jolla has increased 30-fold since 1933. Although Southern California so far has been spared a significant increase in sea level, expectations are that sea level will rise here faster in the coming decades.

Originally published in Catalina Marine Society’s OceanBights, p. 12

References

Peter D. Bromirski, Arthur J. Miller, Reinhard E. Flick, and Guillermo Auad, Dynamical suppression of sea level rise along the Pacific coast of North America: Indications for imminent acceleration

Committee on Sea Level Rise in California, Oregon, and Washington;Board on Earth Sciences and Resources; Ocean Studies Board; Division on Earth and Life Studies; National Research Council, Sea-Level Rise for the Coasts of California, Oregon, and Washington: Past, Present, and Future Committee

Images

1. Increased exposure to coastal flooding along the Los Angeles coastline due to sea level rise: Joe Abraham, adapted from map produced by the The Pacific Institute