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A ‘regime shift’ is happening in the Arctic Ocean, scientists say – Phys.org

Arctic Ocean
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Scientists at Stanford University have discovered a surprising shift in the Arctic Ocean. Exploding blooms of phytoplankton, the tiny algae at the base of a food web topped by whales and polar bears, have drastically altered the Arctic’s ability to transform atmospheric carbon into living matter. Over the past decade, the surge has replaced sea ice loss as the biggest driver of changes in uptake of carbon dioxide by phytoplankton.

The research appears July 10 in Science. Senior author Kevin Arrigo, a professor in Stanford’s School of Earth, Energy & Environmental Sciences (Stanford Earth), said the growing influence of phytoplankton biomass may represent a “significant regime shift” for the Arctic, a region that is warming faster than anywhere else on Earth.

The study centers on net primary production (NPP), a measure of how quickly plants and algae convert sunlight and carbon dioxide into sugars that other creatures can eat. “The rates are really important in terms of how much food there is for the rest of the ecosystem,” Arrigo said. “It’s also important because this is one of the main ways that CO2 is pulled out of the atmosphere and into the .”

A thickening soup

Arrigo and colleagues found that NPP in the Arctic increased 57 percent between 1998 and 2018. That’s an unprecedented jump in productivity for an entire ocean basin. More surprising is the discovery that while NPP increases were initially linked to retreating sea ice, productivity continued to climb even after melting slowed down around 2009. “The increase in NPP over the past decade is due almost exclusively to a recent increase in phytoplankton biomass,” Arrigo said.

Put another way, these microscopic algae were once metabolizing more carbon across the Arctic simply because they were gaining more over longer growing seasons, thanks to climate-driven changes in ice cover. Now, they are growing more concentrated, like a thickening algae soup.

“In a given volume of water, more phytoplankton were able to grow each year,” said lead study author Kate Lewis, who worked on the research as a Ph.D. student in Stanford’s Department of Earth System Science. “This is the first time this has been reported in the Arctic Ocean.”

New food supplies

Phytoplankton require light and nutrients to grow. But the availability and intermingling of these ingredients throughout the water column depend on complex factors. As a result, although Arctic researchers have observed phytoplankton blooms going into overdrive in recent decades, they have debated how long the boom might last and how high it may climb.

By assembling a massive new collection of ocean color measurements for the Arctic Ocean and building new algorithms to estimate phytoplankton concentrations from them, the Stanford team uncovered evidence that continued increases in production may no longer be as limited by scarce nutrients as once suspected. “It’s still early days, but it looks like now there is a shift to greater nutrient supply,” said Arrigo, the Donald and Donald M. Steel Professor in Earth Sciences.

The researchers hypothesize that a new influx of nutrients is flowing in from other oceans and sweeping up from the Arctic’s depths. “We knew the Arctic had increased production in the last few years, but it seemed possible the system was just recycling the same store of nutrients,” Lewis said. “Our study shows that’s not the case. Phytoplankton are absorbing more carbon year after year as new nutrients come into this ocean. That was unexpected, and it has big ecological impacts.”

Decoding the Arctic

The researchers were able to extract these insights from measures of the green plant pigment chlorophyll taken by satellite sensors and research cruises. But because of the unusual interplay of light, color and life in the Arctic, the work required . “The Arctic Ocean is the most difficult place in the world to do satellite remote sensing,” Arrigo explained. “Algorithms that work everywhere else in the world—that look at the color of the ocean to judge how much phytoplankton are there—do not work in the Arctic at all.”

The difficulty stems in part from a huge volume of incoming tea-colored river water, which carries dissolved organic matter that remote sensors mistake for chlorophyll. Additional complexity comes from the unusual ways in which have adapted to the Arctic’s extremely low light. “When you use global satellite remote sensing algorithms in the Arctic Ocean, you end up with serious errors in your estimates,” said Lewis.

Yet these remote-sensing data are essential for understanding long-term trends across an ocean basin in one of the world’s most extreme environments, where a single direct measurement of NPP may require 24 hours of round-the-clock work by a team of scientists aboard an icebreaker, Lewis said. She painstakingly curated sets of ocean color and NPP measurements, then used the compiled database to build algorithms tuned to the Arctic’s unique conditions. Both the database and the algorithms are now available for public use.

The work helps to illuminate how climate change will shape the Arctic Ocean’s future productivity, food supply and capacity to absorb carbon. “There’s going to be winners and losers,” Arrigo said. “A more productive Arctic means more food for lots of animals. But many animals that have adapted to live in a polar environment are finding life more difficult as the ice retreats.”

Phytoplankton growth may also peak out of sync with the rest of the food web because ice is melting earlier in the year. Add to that the likelihood of more shipping traffic as Arctic waters open up, and the fact that the Arctic is simply too small to take much of a bite out of the world’s greenhouse gas emissions. “It’s taking in a lot more carbon than it used to take in,” Arrigo said, “but it’s not something we’re going to be able to rely on to help us out of our climate problem.”



More information:
K.M. Lewis el al., “Changes in phytoplankton concentration now drive increased Arctic Ocean primary production,” Science (2020). science.sciencemag.org/cgi/doi … 1126/science.aay8380

M. Babin el al., “Climate change tweaks Arctic marine ecosystems,” Science (2020). science.sciencemag.org/cgi/doi … 1126/science.abd1231

Citation:
A ‘regime shift’ is happening in the Arctic Ocean, scientists say (2020, July 9)
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Models shift

Models shift to predict dramatically more U.S. deaths as states relax social distancing – POLITICO

The document projects north of 175,000 new cases of Covid-19, the respiratory illness caused by the novel coronavirus, each day. | Carolyn Kaster/AP Photo

A key model of the coronavirus pandemic favored by the White House nearly doubled its prediction Monday for how many people will die from the virus in the U.S. by August – primarily because states are reopening too soon.

The Institute for Health Metrics and Evaluation at the University of Washington’s School of Medicine is now projecting 134,000 coronavirus-related fatalities, up from a previous prediction of 72,000. Factoring in the scientists’ margin of error, the new prediction ranges from 95,000 to 243,000.

Dr. Christopher Murray, the director of IHME, told reporters on a call Monday the primary reason for the increase is many states’ “premature relaxation of social distancing.”

For the first time, Murray explained, the model is factoring in data from four different cell phone providers showing a major uptick in Americans’ going out in public.

This rise of mobility in the last week or 10 days is likely leading to an increase in transmission, he said.

Monday’s update is the fourth since the model debuted in late March. It’s been relied on by the White House in recent months because it presents a more optimistic forecast on health system capacity, cases and deaths than other experts have predicted.

Even with its latest forecast, the University of Washington model is still far more optimistic than a model developed by Johns Hopkins for CDC predicting as many as 3,000 deaths per day by June. Murray said that model, which the New York Times published Monday, is likely inaccurate.

“Our numbers are nowhere near that level,” he said, noting that IHME is forecasting 890 deaths per day by June 1. “This relates very much to whether the models think there is going to be a large, New York-style epidemic in some states. We don’t see that because we’re building into the modeling the rising temperatures and rising testing and contact tracing. That will put the brakes on transmission enough that we won’t see 3,000 deaths a day by June 1.”

In a statement on Monday evening, the Johns Hopkins Bloomberg School of Public Health called the leaked models “preliminary analyses,“ saying that they had been provided to the Federal Emergency Management Agency to help in scenario planning, were not a final version and were not meant to be used or presented as forecasts.

Still, the statement added, “the information illustrates that there are some scenarios, including the premature relaxation of social distancing, that are likely to cause significant increases in the number of COVID-19 cases and deaths in the United States.“

The White House on Monday acknowledged the existence of the internal administration document but asserted that the grim modeling had not gone through interagency vetting and “is not reflective” of any projections from or analyzed by the White House coronavirus task force.

In a statement to reporters, White House deputy press secretary Judd Deere said that the internal report obtained by The New York Times was “not a White House document” and hadn’t been presented to the coronavirus task force.

The CDC document projects north of 175,000 new cases of Covid-19, the respiratory illness caused by the novel coronavirus, each day. That’s up from about 25,000 new cases per day last week and more than four times the peak of about 37,000 new cases per day.

The alarming modeling comes as some states are already beginning to put parts of the White House’s phased reopening plan into motion despite concerns that the administration’s guidelines for doing so have not yet been met. It also underscores fears that moving too fast to relax strict social-distancing restrictions could fuel a dangerous second wave of infections.

The CDC document found some reason for optimism, noting that nationwide, the trajectory of new illnesses in “multiple counties, including hard hit areas in Louisiana and in the New York City region” has continued to decrease, and that incidence rates have recently plateaued around Chicago.

Still, it found that there “remains a large number of counties whose burden [of illness] continues to grow or are in an elevated incidence plateau, including in the Great Lakes region, parts of the Southeast, Northeast, and around southern California.” The document includes a color-coded map of the country with darker spots peppered throughout, and it states that the goal “is to have all communities be represented in the lighter colors, demonstrating little to no disease burden and no increase in trajectory.”

Deere on Monday defended the White House plan, which President Donald Trump released last month with the goal of returning to some semblance of normalcy and reviving an economy that has been shuttered over the past two months due to the virus.

The guidelines “are a scientific driven approach that the top health and infectious disease experts in the federal government agreed with,” Deere said. “The health of the American people remains President Trump’s top priority and that will continue as we monitor the efforts by states to ease restrictions.”

Murray also noted that the updated University of Washington model also now takes into account the ramping up of testing in most states, as well as warming temperatures heading into late spring and early summer. But he cautioned that the impact of temperature on coronavirus transmission is not yet fully understood, and likely will not be for several more months.

For now, IHME is assuming that every degree Celsius the temperature goes up will lead to a 2 percent decline in transmission.

“Are we sure about that? No,” he said.