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August GeoRoundUp: the best of the Earth sciences from around the web

August GeoRoundUp: the best of the Earth sciences from around the web

Drawing inspiration from popular stories on our social media channels, as well as unique and quirky research news, this monthly column aims to bring you the best of the Earth and planetary sciences from around the web.

Major Stories

On August 25th Hurricane Harvey made landfall along the southern coast of the U.S.A, bringing record breaking rainfall, widespread flooding and a natural disaster on a scale not seen in the country for a long time. In fact, it’s the first time since 2005 a major hurricane has threatened mainland U.S.A. – a record long period.

But Harvey’s story began long before it brought destruction to Texas and Louisiana.

On August 17th,the National Space Agency (NASA) satellite’s first spotted a tropical depression forming off the coast of the Lesser Antilles. From there the storm moved into the eastern Caribbean and was upgraded to Tropical Storm Harvey where it already started dropping very heavy rainfall. By August 21st, it had fragmented into disorganised thunderstorms and was spotted near Honduras, where heavy local rainfall and gusty winds were predicted.

Over the next few days the remnants of the storm travelled westwards towards Nicaragua, Honduras, Belize and the Yucatan Peninsula. Forecasters predicted that, owing to warm waters of the Gulf of Mexico and favorable vertical wind shear, there was a high chance the system could reform once it moved into the Bay of Campeche (in the southern area of the Gulf of Mexico) on August 23rd. By August 24th data acquired with NASA satellites showed Harvey had began to intensify and reorganise. Heavy rainfall was found in the system.

Harvey continued to strengthen as it traveled across the Gulf of Mexico and weather warnings were issued for the central coast of Texas. Citizens were told to expect life-threatening storm surges and freshwater flooding. On August 25th, Harvey was upgraded to a devastating Category 4 hurricane, when sustained wind speeds topped 215 kph.

Since making landfall on Friday and stalling over Texas (Louisiana is also affected) – despite being downgraded to a tropical storm as it weakened – it has broken records of it’s own. “No hurricane, typhoon, or tropical storm, in all of recorded history, has dropped as much water on a single major city as Hurricane Harvey is in the process of doing right now in Houston (Texas)”, reports Forbes. In fact, the National Weather Service had to update the colour charts on their graphics in order to effectively map it. This visualisation maps Harvey’s destructive path through Texas.

A snaptshot from the tweet by the official Twitter account for NOAA’s National Weather Service.

So far the death toll is reported to be between 15 to 23 people, with the Houston Police Chief saying 30,000 people are expected to need temporary shelter and 2,000 people in the city had to be rescued by emergency services (figures correct at time of writing).

Many factors contributed toward making Hurricane Harvey so destructive. “The steering currents that would normally lift it out of that region aren’t there,” J. Marshall Shepherd, director of the atmospheric sciences program at the University of Georgia, told the New York Times. The storm surge has blocked much of the drainage which would take rainfall away from inland areas. And while it isn’t possible to say climate change caused the hurricane, “it has contributed to making it worse”, says Michael E Mann. The director of the Earth System Science Center at Pennsylvania State University argues that rising sea levels and ocean water temperatures in the region (brought about by climate change) contributed to greater rainfall and flooding.

A man carries his cattle on his shoulder as he moves to safer ground at Topa village in Saptari. Credit: The Guardian.

While all eyes are on Houston, India, Bangladesh and Nepal are also suffering the consequences of devastating flooding brought about a strong monsoon. The United Nations estimates that 41 million people are affected by the disaster across the three countires. Over 1200 people are reported dead. Authorities are stuggling with the scale of the humanitarian crisis: “Their most urgent concern is to accessing safe water and sanitation facilities,” the UN Office for the Coordination of Humanitarian Affairs (OCHA) said earlier this week, citing national authorities. And its not only people at risk. Indian authorities reported large swathes of a famous wildlife reserve park have been destroyed. In Mumbai, the downpour caused a building to collapse killing 12 people and up to 25 more are feared trapped.Photo galleries give a sense of the scale of the disaster.

Districts affected by flooding. Credit: Guardian graphic | Source: ReliefWeb. Data as of 29 August 2017

What you might have missed

In fact, it’s highly unlikely you missed the coverage of this month’s total solar eclipse over much of Northern America. But on account of it being the second biggest story this month, we felt it couldn’t be left out of the round-up. We particularly like this photo gallery which boasts some spectacular images of the astronomical event.

This composite image, made from seven frames, shows the International Space Station, with a crew of six onboard, as it transits the Sun at roughly five miles per second during a partial solar eclipse, Monday, Aug. 21, 2017 near Banner, Wyoming. Credit: (NASA/Joel Kowsky)

Since the end of July, wildfires have been raging in southwest Greenland. While small scale fires are not unheard of on the island otherwise known for its thick ice cap and deep fjords, the fires this month are estimated to extend over 1,200 hectares. What started the fires remains unknown, as do the fuel sources and the long-term impacts of the burn.

The U.S.A’s National Oceanic and Atmospheric Administration highlighted that the fires are a source of sooty “black carbon”. As the ash falls on the pristine white ice sheet, it turns the surface black, which can make it melt faster. Greenland police recently reported that unexpected rain haf all but extinguished the massive fires; though the situation continues to be monitored, as smouldering patches run the risk of reigniting the flames.

 

 

 

Links we liked

The EGU story

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From today, until 8 Sep 2017, you can suggest:

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Imaggeo on Mondays: Iceberg at midnight

Standing on the vast expanse of gleaming white sea ice of the Atka Bay, Michael Bock took this stunning picture of an Antarctic iceberg. The days, during the Antarctic summer, are never ending. Despite capturing the image at midnight, Michael was treated to hazy sunlight.

Icebergs at midnight. Credit: Michael Bock (distributed via imaggeo.egu.eu)

Icebergs at midnight. Credit: Michael Bock (distributed via imaggeo.egu.eu)

“Clearly visible [in the iceberg] are the annual snow accumulation layers which illustrate how the ice archive works.; as you look down the icy face, the ice gets older,” explains Michael. As more snow accumulates on the surface of the glacier, the underlying layers of snow are compressed by the weight from above, hence layers become thinner with increasing depth. On the ice shelf or on the Antarctic plateau these accumulation layers can only be seen when digging a snow pit. The obvious limitation of this is that only a few meters can be excavated with spades, limiting the observations one can carry out. Instead, to gain information about what happens deep within the ice pack, drill cores are usually used. Long cores of the layers of ice can be extracted , providing useful data. “One can drill into the ice (typically on the Antarctic plateau on ice divides or domes) reaching down to bedrock, with the retrieved ice core revealing long records of climatic history,” adds Michael. Deep ice cores can be more than 3000 m long. Depending on e.g. annual mean temperature and accumulation rate the age and resolution of these archives can vary greatly. Whilst this iceberg cannot be studied directly due to hazards associated with working underneath it does “serve as a beautiful visualisation of what we are searching for in ice core science”, explains Michael.

By Laura Roberts Artal and Michael Bock.

If you pre-register for the 2015 General Assembly (Vienna, 12 – 17 April), you can take part in our annual photo competition! From 1 February up until 1 March, every participant pre-registered for the General Assembly can submit up three original photos and one moving image related to the Earth, planetary, and space sciences in competition for free registration to next year’s General Assembly!  These can include fantastic field photos, a stunning shot of your favourite thin section, what you’ve captured out on holiday or under the electron microscope – if it’s geoscientific, it fits the bill. Find out more about how to take part at http://imaggeo.egu.eu/photo-contest/information/.

Geosciences column: Playing back the Antarctic ice records

Satellites are keeping tabs on the state of Arctic and Antarctic sea ice, and have observed considerable declines in ice extent in many areas since records began, but what do we know of past sea ice extent?

Ice cores keep an excellent record of climate change, but until recently, ice cores have not been used to quantify patterns in past sea ice extent because few reliable compounds are preserved in the ice. While methanesulphonic acid (MSA) has been used in the past, it is an unstable compound and is easily remobilised after it has been deposited. The amount of sea-salt sodium deposited in brine pools or as high salinity crystals known as ‘frost flowers’ that form on the ice surface can also be used to identify changes in sea ice extent. These deposits are difficult to distinguish from larger sources of sea-salt sodium (aerosols and sea spray) though, making it a poor proxy.

Recent research published in Atmospheric Chemistry and Physics may provide an answer. An international team of geochemists have identified two stable indicators of sea ice extent in ice cores: the halogens bromine and iodine.

The oceans are considered to the be the main reservoir of bromine and iodine, but satellite data show these halogens also have a strong link with sea ice at the poles. Furthermore, recent research suggests that algae that grow under sea ice are big contributors to atmospheric iodine. Sea ice provides a substrate for algae to grow on during the spring. It is thin enough for light to penetrate, allowing the algae to photosynthesise, and also allows compounds produced by the algae to reach the atmosphere, including iodine and iodine oxide. These peaks in iodine oxide production are spotted by satellites during the spring.

The underside of Antarctic pack ice. The brown-green algae are an important food source for krill, as well as being a source of atmospheric iodine. (Credit: Kills and Marshall, 1995)

The underside of Antarctic pack ice. The brown-green algae are an important food source for krill, as well as being a source of atmospheric iodine. (Credit: Kills and Marshall, 1995)

During interglacials, the extent of sea ice is much smaller than during a glacial period. This means that the thin sea ice (where iodine is released into the atmosphere) is much closer to the coast. Air bubbles trapped in compacting continental snow preserve these atmospheric gases, which can be sampled in an ice core at a much much later date. Thus, when there is more iodine in the ice core, the extent of sea ice is small; when there is less, the thin edge of the ice sheet was much further from the coast.

Satellite measurements also show the amount of bromine oxide in the atmosphere peaks during the polar spring. This is because the increase in light level stimulates a series of photochemical reactions that convert bromine salts into bromine and bromine oxide, releasing it into the atmosphere. These events are known as bromine explosions and result in an increase in atmospheric bromine.

How bromine ions (bromide) makes it way from the ocean to the atmosphere and onto the surface of Antarctica (where it is later compacted by layers of snow, forming ice, and drilled to produce the Talos Dome ice core). Blue, red and green lines indicate aerosol-phase bromide, gas-phase bromide and hydrogen bromide, respectively. (Credit: Spolaor et al., 2013)

How bromine ions (bromide) makes it way from the ocean to the atmosphere and onto the surface of Antarctica (where it is later compacted by layers of snow, forming ice, and drilled to produce the Talos Dome ice core). Blue, red and green lines indicate aerosol-phase bromide, gas-phase bromide and hydrogen bromide, respectively (click for larger). (Credit: Spolaor et al., 2013)

Because the extent of sea ice is reduced during interglacials, bromine explosions must occur closer to the Antarctic coast, meaning more bromine will be trapped in the ice sheet during an interglacial period. Using sodium as a proxy for the amount of sea salt in the ice core, Andrea Spolaor and her team were able to work out how much of the bromine was in the atmosphere at the time. Since bromine explosions result in an an increase in atmospheric bromine, but have no effect on sodium, these events can be identified when the ratio of bromine to sodium in the ice core is high.

Now we can work out the extent of past sea ice, what lies ahead? The first part of the IPCC 5th Assessment Report released earlier today concerns the physical changes in the Earth’s climate and what we can expect in the future; the future of our changing planet will be discussed at this year’s Geosciences Information For Teachers workshop at EGU 2014, and you will be able to find a great discussion of climate change, its history and its impacts in the next issue of GeoQ – stay tuned!

By Sara Mynott, EGU Communications Officer

Reference:

Spolaor, A., Vallelonga, P., Plane, J. M. C., Kehrwald, N., Gabrieli, J., Varin, C., Turetta, C., Cozzi, G., Kumar, R., Boutron, C., and Barbante, C.: Halogen species record Antarctic sea ice extent over glacial–interglacial periods, Atmos. Chem. Phys., 13, 6623-6635, 2013.

Geosciences Column: Autofluorescence in polar regions – how and why?

Marine picoplankton, <2 µm, are one of the most ubiquitous fauna in the open ocean. These marine microorganisms are hugely important – being responsible for a significant proportion of oceanic net primary productivity. Researchers are able to track the evolution of their genomes and the transportation of these microorganisms by analysing ice cores, which offer the potential to study the evolution of marine bacteria over approximately 300 million generations, equivalent to the last 700,000 years.

A team from Berkeley, P.B. Price and R.C. Ray, set out to map autofluorescence of chlorophyll (Chl) and the amino acid tryptophan (Trp) using fluorescence spectrometry.  Autofluorescence is the ability of biological structures, such as mitochondria, to emit natural light once they have absorbed light from another source. In addition, amino acids like tryptophan show some degree of autofluorescence.

The purpose of the Berkeley study was to measure chlorophyll (Chl) and tryptophan (Trp), both of which are found in the cell walls of phytoplankton and bacteria, as a function of depth in Greenland and Antarctic ice cores. These allow scientists to measure microbial activity within a body of water and as such the biological oxygen demand. To do this they used a Scanning Fluorescence Spectrometer in the dark at -25 °C. They found that autofluorescing compounds decrease only marginally (by a factor of three) in depths in excess of ~2300 m, and that there is a clear see-saw pattern between summer and winter production, varying by about 25%.

To undertake the majority of their experiments the team used the Berkeley Fluorescence Spectrometer (BFS) to excite fluorescence in an ice core with a smoothly planed surface. In addition, they also carried out Flow Cytometric (FCM) analysis of samples cut and melted from ice cores taken from various locations on the Greenland and Antarctic ice sheets. FCM provides rapid and accurate measurements of individual phytoplanktonic cells that are too dim to be discriminated using epifluorescence microscopy, and is well suited to study the smallest size class of the plankton (<2 µm).

Their initial results reveal that cells containing Chl ecotypes (varieties specific to a particular set of environmental conditions) undergo photobleaching in air. This can complicate the observation of fluorescent molecules since they will eventually be destroyed by the light exposure that initially causes them to fluoresce, like that from a microscope beam. Furthermore, based on FCM analysis, the decline in Chl is not due to a gradual decrease of Chl autofluorescence per cell over time in the ice-bound phototrophs (organisms that carry out photon capture to acquire energy, and use the energy from light to carry out various cellular metabolic processes). It is possible then that cyanobacteria that adapt to compaction from surface snow into ice without disruption may recover from sunlight bleaching. So what was the cause?

Chl autofluorescence (arbitrary units) at several depths in ice cores showing fluctuations consistent with summer-winter variations. (A) Chl and Trp over 4 yr in Western Antarctic Ice Sheet Divide ice (WAISD), summer maxima are marked with arrows; (B) Chl in Greenland ice shows maxima during 3 summers, wiggly red line is a spline fit to the data, blue arrow indicates general decrease in chlorophyll (Modified from Price and Bay 2013).

Chl autofluorescence (arbitrary units) at several depths in ice cores showing fluctuations consistent with summer-winter variations. (A) Chl and Trp over 4 yr in Western Antarctic Ice Sheet Divide ice (WAISD), summer maxima are marked with arrows; (B) Chl in Greenland ice shows maxima during 3 summers, wiggly red line is a spline fit to the data, blue arrow indicates general decrease in chlorophyll (Modified from Price and Bay 2013).

To determine whether Chl autofluorescence in the ice came from Chl in cells they used differential interference contrast microscopy and epifluorescence microscopy to search for microorganisms in melted, unstained, samples across both polar regions. Therefore, the strong Chl emission, its annual modulation in the ice cores, and the absence of Chl autofluorescence seen might be due to the presence of picocyanobacteria belonging to the genera Prochlorococcus (Pro) and Synechococcus (Syn). Buford Price comments,

“Using flow cytometry, we find that every sample of more than ~10 g of ice contains enough Pro and Syn cells that we can plot their concentration vs depth and vs location in Antarctic or Greenland ice. We can use the sorting ability of some flow cytometers to deflect only the Prochlorococcus and Synechococcus cells into sterile vials for later analysis of their DNA or for culturing”.

Syn cells are found over a much wider range than Pro cells, typically extending from pole-to-pole near nutrient-rich water, but do not extend significantly downward in the photic zone. In contrast, Pro cells have yet to be identified outside of 40°N and 40°S, and do extend down to 150 m in the photic zone. Price and Bay attribute the decrease in Chl and picocyanobacteria concentration from summer to winter to the combined effects of lower ocean temperatures and decreased daylight at latitudes populated by both Pro and Syn.

For Pro and Syn to be present at all depths in Arctic and Antarctic ice, and with a summer-winter concentration difference of only ~25%, they must have grown in waters at lower latitudes before being transported by wind and ocean currents to higher latitudes. An important discovery is that when Pro and Syn-like cells are deposited onto fresh snow and frozen into ice, FCM measurements show no obvious decrease in autofluorescence with time, with Buford Price commenting that their ultimate,

“…goal is to map changes in Pro and Syn genomes with depth and this with time in the past. This will work because at typical ice temperature at different depths (-30 to -40 C) the DNA degrades extremely slowly if the ice is reasonably pure and devoid of mineral rocks that might contain radioactive impurities” (personal communication).

This is an example of a protective feature of glacial ice that preserves Chl and other pigments in phototrophs against losing autofluorescence intensity with time in total darkness.

Their results suggest that Pro and Syn cells are transported by hemispheric wind patterns, from oceans at temperate latitudes. It is thus highly plausible that there is an annual modulation, between summer and winter. The team admit that it is very challenging to accurately model the fluxes of wind-borne Pro and Syn cells that reach the polar regions from the mid-latitudes, but the evidence that they’re transported here is convincing and presents a worthy challenge to the prevailing hypothesis that they originated separately in polar lakes.

By Alexander Stubbings, Freelance Science Writer

Reference:

Price, P. B. and Bay, R. C.: Marine bacteria in deep Arctic and Antarctic ice cores: a proxy for evolution in oceans over 300 million generations, Biogeosciences, 9, 3799-3815, 2012