Massive Reef Found at Mouth of the Amazon

The changes that the Amazon River promotes in the tropical North Atlantic ocean water make an unfavorable environment for reef development. Every second, 175 million liters of water mixed with sediments are brought to the ocean. The result is low sunlight penetration, variability in nutrient concentration, salinity and pH, extensive moody bottoms and significant changes in temperature and oxygenation levels towards the bottom - conditions not associated with reefs. The plume generated by the Amazon River has 1.3 million km2 and flows mostly to the North, reaching areas as far as the Caribbean Sea.

Against all the odds, 39 scientists from nine Brazilian and one North-American universities mobilized two expeditions to the mouth of the river in other to map the bottom of the ocean in the outer shelf. Two previous studies - from the 1970s and 1980s - reported the findings of single samples of carbonatic structures. None suggested the existence of a reef system underneath the river plume. Surprisingly, the researchers found reefs in a complex as extensive as 1,000 km, in depths from 10 to 120 meters, with rhodolith beds, live calcareous algae, sponges, corals and hydrocorals colonies formed from 13,000 years ago till the present. The system is an habitat for 73 species of fishes and six species of lobsters.

link.

The Inferred Aptian Cretaceous Paleoceanography of the South Atlantic

Late Aptian (Cretaceous) paleoceanography of the South Atlantic Ocean inferred from dinocyst communities of the Sergipe Basin

Authors:

Carvalho et al

Abstract:

The late Aptian (Early Cretaceous) is a crucial time interval for understanding the paleoceanographic changes in the Southern Hemisphere. Oceanographic changes in the emerging South Atlantic Ocean during this interval are reflected in the stratigraphic distribution of dinoflagellate communities recorded in the Muribeca and Riachuelo formations of the Sergipe Basin in northeastern Brazil. The Subtilisphaera community, in the lower and middle parts of the section, appears to be related to the Subtilisphaera Ecozone and suggests the onset of Tethyan influence in the central South Atlantic, in a restricted to inner-neritic environment. The succeeding Spiniferites community, in the middle part of the section, represents the first significant transgression, probably of eustatic origin. The Cyclonephelium-Exochosphaeridium community, in the upper part of the section, appears to be related to an oceanic event characterized by intermittent dysoxic-anoxic conditions. The uppermost part of the section is dominated by the Spiniferites community, related to a progressive regional transgression and culminating in an open-marine, fully Tethyan environment in the central part of the widening South Atlantic.

Why the Atlantic Ocean was More Acidified During the Paleocene Eocene Thermal Maximum

Around 55 million years ago, an abrupt global warming event triggered a highly corrosive deep-water current through the North Atlantic Ocean. The current's origin puzzled scientists for a decade, but an international team of researchers has now discovered how it formed and the findings may have implications for the carbon dioxide emission sensitivity of today's climate.

The researchers explored the acidification of the ocean that occurred during a period known as the Paleocene Eocene Thermal Maximum (PETM), when the Earth warmed 9 degree Fahrenheit in response to a rapid rise in carbon dioxide in the atmosphere and subsequently one of the largest-ever mass extinctions occurred in the deep ocean. They report their findings in today's (May 11) issue of Nature Geoscience.

This period closely resembles the scenario of global warming today.

"There has been a longstanding mystery about why ocean acidification caused by rising atmospheric carbon dioxide during the PETM was so much worse in the Atlantic compared to the rest of the world's oceans," said lead author Kaitlin Alexander, ARC Centre of Excellence for Climate System Science, University of New South Wales, Australia. "Our research suggests the shape of the ocean basins and changes to ocean currents played a key role in this difference. Understanding how this event occurred may help other researchers to better estimate the sensitivity of our climate to increasing carbon dioxide."

To get their results the researchers recreated the ocean basins and land masses of 55 million years ago in a global climate model.

During that time a ridge on the ocean floor existed between the North and South Atlantic that separated the deep water in the North Atlantic from the rest of the world's oceans. The ridge was like a giant bathtub on the ocean floor.

The simulations showed this ridge became filled with extremely corrosive water from the Arctic Ocean, which mixed with dense salty water from the Tethys Ocean and sank to the seafloor, where it accumulated. The sediment in this area indicates the water was so corrosive that it dissolved all the calcium carbonate produced by organisms that settled on the ocean floor.

When the Earth warmed as a result of a rapid increase in atmospheric carbon dioxide, it eventually warmed this corrosive bottom water. As this water warmed it became less dense and denser water sinking from above replaced it. The corrosive deep water was pushed up and spilled over the edge of the giant "bathtub" and flowed into the South Atlantic.

link.

Evidence of the Middle Eocene Climatic Optimum From the South-East Atlantic

The Middle Eocene Climatic Optimum (MECO): A multi-proxy record of paleoceanographic changes in the South-East Atlantic (ODP Site 1263, Walvis Ridge)

Authors:

Boscolo Galazzo et al

Abstract:

The Middle Eocene Climatic Optimum (MECO, ~40 Ma) was a transient period of global warming that interrupted the secular Cenozoic cooling trend. We investigated the paleoceanographic, paleoenvironmental and paleoecological repercussions of the MECO in the south-east Atlantic subtropical gyre (Ocean Drilling Program Site 1263). TEX86 and δ18O records support an ~4 °C increase in surface and deep-water temperatures during the MECO. There is no long-term negative carbon isotope excursion (CIE) associated with the early warming, consistent with other sites, and there is no short-term negative CIE (~50 kyr) during the peak of the MECO, in contrast to what has been observed at some sites. This lack of a CIE during the peak of the MECO at Site 1263 could be due to poor sediment recovery or geographic heterogeneity of the δ13C signal. Benthic and planktic foraminiferal mass accumulation rates declined markedly during MECO, indicating a reduction of planktic foraminiferal production and export productivity. Vertical δ13C gradients do not indicate major changes in water-column stratification, and there is no biomarker or micropaleontological evidence that hypoxia developed. We suggest that temperature-dependency of metabolic rates could explain the observed decrease in foraminiferal productivity during warming. The kinetics of biochemical reactions increase with temperature, more so for heterotrophs than for autotrophs. Steady warming during MECO may have enhanced heterotroph (i.e., foraminiferal) metabolic rates, so that they required more nutrients. These additional nutrients were not available because of the oligotrophic conditions in the region and the lesser response of primary producers to warming. The combination of warming and heterotroph starvation altered pelagic food webs, increased water-column recycling of organic carbon, and decreased the amount of organic carbon available to the benthos.

Atlantic Circulation Currents Slowing Down

A ‘global conveyor belt’ stirs the oceans from top to bottom, with surface currents transporting warm water to the poles while cold water in the depths flows back to the tropics. But it operates in fits and starts, with the strength of the currents varying widely. Eager for a better understanding of how the vagaries of the conveyor belt shape weather and climate, oceanographers are planning two new large-scale projects to watch over Atlantic currents.

An array of instruments between Florida and the Canary Islands has been continuously monitoring the strength of the North Atlantic portion of the global conveyor belt since 2004. In December, if all goes well, an international project led by the United States will begin another set of continuous measurements of the Atlantic Meridional Overturning Circulation (AMOC), using an array of sensors strung between South Africa and Argentina. And this month, US and British funding agencies are set to decide whether they will support a new surface-to-bottom monitoring array between Labrador in Canada and Scotland, UK. The United Kingdom will also decide whether to continue operating the existing array.

Expanding such monitoring is crucial if scientists are to improve seasonal weather and climate forecasts, says Harry Bryden, an oceanographer at the University of Southampton, UK. Components of the AMOC, such as the Gulf Stream, ferry vast amounts of heat from the tropics to high latitudes, heating the winds that keep Europe’s climate mild. As a result, year-to-year and longer-term changes in the strength of these currents can affect seasonal conditions across much of Europe, Africa, South America and North America.

link.

Productivity and Sea Surface Temperature Changes Across the Eocene/Oligocene Paleogene Boundary in the South Atlantic

Productivity and sea-surface temperature changes recorded during the late Eocene-early Oligocene at DSDP Site 511 (South Atlantic)

Authors:

Plancq et al

Abstract:

This study investigates paleoenvironmental changes during the Eocene-Oligocene transition (EOT) at Deep Sea Drilling Project (DSDP) Site 511 (South Atlantic), as inferred from lipid biomarker (long-chain diols, alkenones) and calcareous nannofossil accumulation rates, as well as changes in sedimentation regime (i.e. relative contributions of total organic carbon-TOC-, calcium carbonate, and biogenic silica). Sea-surface temperatures (SSTs) reconstructed from the alkenone unsaturation index UK’37 indicate a progressive but significant cooling (~ 8°C) from 34.5 Ma to 33.6 Ma, consistent with estimates derived from other temperature proxies (TEX86; δ18O) at the same site and for the same time interval. This cooling is associated with a marked increase in primary productivity, as indicated by high accumulation rates of biogenic silica, TOC, alkenones, long-chain diols, and calcareous nannofossils. Together, these results are consistent with an enhancement of upwelling conditions favorable to the development of siliceous organisms at DSDP Site 511, possibly induced by the Oi-1 glaciation in Antarctica that occurred during this period.

Model Predicts Less Storms like Sandy

Model projections of atmospheric steering of Sandy-like superstorms

Authors:

1. Elizabeth A. Barnes (a,b)
2. Lorenzo M. Polvani (b,c)
3. Adam H. Sobel (b,c)

Affiliations:

a. Department of Atmospheric Science, Colorado State University, Fort Collins, CO 80523;

b. Division of Ocean and Climate Physics, Lamont-Doherty Earth Observatory, Palisades, NY 10964; and

c. Department of Applied Physics and Applied Mathematics and Department of Earth and Environmental Sciences, Columbia University, New York, NY 10027

Abstract:

Superstorm Sandy ravaged the eastern seaboard of the United States, costing a great number of lives and billions of dollars in damage. Whether events like Sandy will become more frequent as anthropogenic greenhouse gases continue to increase remains an open and complex question. Here we consider whether the persistent large-scale atmospheric patterns that steered Sandy onto the coast will become more frequent in the coming decades. Using the Coupled Model Intercomparison Project, phase 5 multimodel ensemble, we demonstrate that climate models consistently project a decrease in the frequency and persistence of the westward flow that led to Sandy’s unprecedented track, implying that future atmospheric conditions are less likely than at present to propel storms westward into the coast.

Extinction of Sirenia of Europe and North Africa

The disappearance of the European/North African Sirenia (Mammalia)

Authors:

1. Gonçalo Prista (a)
2. Mário Estevens (c)
3. Rui Agostinho (d)
4. Mário Cachão (a, b)

Affiliations:

a. Centre of Geology of the University of Lisbon, Campo Grande, 1749-016 Lisbon, Portugal

b. Faculty of Sciences of the University of Lisbon, Geology Department, Campo Grande, 1749-016 Lisbon, Portugal

c. Almada City Council, Departamento de Estratégia e Gestão Ambiental Sustentável Ecoteca de Almada - Casa Municipal do Ambiente R. Bernardo Francisco da Costa, nº 40 e nº 42 2800-029 Almada, Portugal

d. Faculty of Sciences of the University of Lisbon, Physics Department, Campo Grande, 1749-016 Lisbon, Portugal

Abstract:

Sirenia inhabited the coastal waters of Europe and North Africa from the Eocene until the end of the Pliocene. They are the only herbivorous marine mammals, and their presence in the European/North African realm is supported by almost 400 fossil records. Their dependence on seagrass, as well as their ecological needs, limited their capability to adapt to the climate changes that occurred during the Cenozoic. Their disappearance from European and Mediterranean shores occurred in two different steps: 1) the European Atlantic extinction, related to global cooling and fragmentation of the seagrass meadows, which greatly reduced sirenia habitats and resources; 2) their disappearance from the Mediterranean, linked not to declining resources but to the onset of continental glaciations in the northern hemisphere.

The Influence of the Amazon River on the Miocene Neogene Central American Seaway

Influence of the Amazon River development and constriction of the Central American Seaway on Middle/Late Miocene oceanic conditions at the Ceara Rise

Authors:

1. S. Heinrich (a)
2. K.A.F. Zonneveld (a, b)

Affiliations:

a. Department of Geosciences, University of Bremen, P.O. Box 330 440, D-28334 Bremen, Germany

b. MARUM, Center for Marine environmental Sciences, University of Bremen, Leobener Straße, D-28359 Bremen, Germany

Abstract:

Sediment samples from ODP 154 Site 926A (Ceara Rise, western equatorial Atlantic Ocean) spanning the Neogene from 12.8 to 9.2 Ma were investigated on their calcareous dinoflagellate contents to better understand the oceanographic changes in relation to the closure of the Central American Seaway and the development of the Amazon River. Intervals with increased cyst accumulation rates and dissolution sensitive species occur from 12.4 Ma onward. They correspond to periods of enhanced North Atlantic Deep Water production indicating the presence of this water mass at the research site during these intervals. This suggests that pulses of North Atlantic Deep waters sporadically flew into the South Atlantic related to uplift phases of the Panama Sill.

At about 11.2 Ma the first appearance of Leonella granifera indicates river influence at the sample site. This first indication of river influence in the western equatorial Atlantic can be linked to the developing Amazon River. The cyst association changes at about 11.2 Ma from almost monospecific to highly diverse and the permanent presence and increased abundance of L. granifera suggests that river waters were able to reach the study site by now, probably as a result of the southward flowing North Brazil Current. After 10.5 Ma the cyst association indicates a decrease in Amazon influence at Site 926A. This change can be correlated to a reducing inflow of Pacific waters through the Central American Seaway leading to a reverse of the North Brazil Current to its modern northwards flow pattern.

Supercontinent Cycle: Has the Atlantic Started to Close?

Hundreds of millions of years ago, a single mega-continent on the Earth broke up and began to drift apart. The pieces spread out across the surface of the globe, eventually settling in their current positions as continents and creating oceans in between. Now scientists have observed the first indication that this movement may be shifting into reverse, setting the United States and Europe on an eventual collision course.

Such an expansion and contraction of the Earth’s crust is directed by a recurring process called the Wilson cycle. Step one: tectonic plates move apart, breaking up supercontinents and filling oceans. (Picture Pangea.) Step two: tectonic plates fracture, creating new subduction zones that force one plate under the other, into the Earth’s molten mantle. Step three: subduction brings the continents back together to create a new supercontinent.

Paper link.

Draining of Lake Agassiz Caused Younger Dryas Snap Freezing

Caption: A new model of flood waters from melting of the Laurentide Ice Sheet and large glacial lakes along its edge that covered much of North America from the Arctic south to New England over 13,000 years ago, shows the meltwater flowed northwest into the Arctic first. This weakened deep ocean circulation and led to Earth’s last major cold period. A new model of flood waters from melting of the Laurentide Ice Sheet and large glacial lakes along its edge that covered much of North America from the Arctic south to New England over 13,000 years ago, shows the meltwater flowed northwest into the Arctic first. This weakened deep ocean circulation and led to Earth’s last major cold period.

For more than 30 years, climate scientists have debated whether flood waters from melting of the enormous Laurentide Ice Sheet, which ushered in the last major cold episode on Earth about 12,900 years ago, flowed northwest into the Arctic first, or east via the Gulf of St. Lawrence, to weaken ocean thermohaline circulation and have a frigid effect on global climate.

Now University of Massachusetts Amherst geoscientist Alan Condron, with Peter Winsor at the University of Alaska, using new, high-resolution global ocean circulation models, report the first conclusive evidence that this flood must have flowed north into the Arctic first down the Mackenzie River valley. They also show that if it had flowed east into the St. Lawrence River valley, Earth's climate would have remained relatively unchanged.

"This episode was the last time the Earth underwent a major cooling, so understanding exactly what caused it is very important for understanding how our modern-day climate might change in the future," says Condron of UMass Amherst's Climate System Research Center. Findings appear in the current issue of Proceedings of the National Academy of Sciences.

Events leading up to the sharp climate-cooling period known as the Younger Dryas, or more familiarly as the "Big Freeze," unfolded after glacial Lake Agassiz, at the southern edge of the Laurentide ice sheet covering Hudson Bay and much of the Canadian Arctic, catastrophically broke through an ice dam and rapidly dumped thousands of cubic kilometers of fresh water into the ocean.

This massive influx of frigid fresh water injected over the surface of the ocean is assumed to have halted the sinking of very dense, saltier, colder water in the North Atlantic that drives the large-scale ocean circulation, the thermohaline circulation, that transports heat to Europe and North America. The weakening of this circulation caused by the flood resulted in the dramatic cooling of North America and Europe.

Using their high resolution, global, ocean-ice circulation model that is 10 to 20 times more powerful than previously attainable, Condron and Winsor compared how meltwater from the two different drainage outlets was delivered to the sinking regions in the North Atlantic. They found the original hypothesis proposed in 1989 by Wally Broecker of Columbia University suggesting that Lake Aggasiz drained into the North Atlantic down the St. Lawrence River would have weakened the thermohaline circulation by less than 15 percent.

Condron and Winsor say this level of weakening is unlikely to have accounted for the 1,000-year cold climate event that followed the meltwater flood. Meltwater from the St. Lawrence River actually ends up almost 1,900 miles (3,000 km) south of the deep water formation regions, too far south to have any significant impact on the sinking of surface waters, which explains why the impact on the thermohaline circulation is so minor.

By contrast, Condron and Winsor's model shows that when the meltwater first drains into the Arctic Ocean, narrow coastal boundary currents can efficiently deliver it to the deep water formation regions of the sub-polar north Atlantic, weakening the thermohaline circulation by more than 30 percent. They conclude that this scenario, showing meltwater discharged first into the Arctic rather than down the St. Lawrence valley, is "more likely to have triggered the Younger Dryas cooling."

Condron and Windor's model runs on one of the world's top supercomputers at the National Energy Research Science Computing Center in Berkeley, Calif. The authors say, "With this higher resolution modeling, our ability to capture narrow ocean currents dramatically improves our understanding of where the fresh water may be going."

People ask me what we run on our dayjob supercomputers. Well. There ya go.

Time Lapse of Sandy Hitting Manhattan

Greenland is Dumping Freshwater into the North Atlantic...and its Implications

In a new study lead by Jonathan Bamber, scientists found that, over the past few decades, the melting of Greenland glaciers has been feeding an anomalous spike in North Atlantic freshwater. If it continues as it has been, in the coming years the spike will rival the effects of the Great Salinity Anomaly—a bulge of fresh water that can affect the circulation patterns of the whole Atlantic Ocean.

Here’s the background: In the late 1960s, the first Great Salinity Anomaly (GSA) formed off the eastern shores of Greenland. Formed by a spike in Arctic ice melt, the event led to the formation of a thin sheet of fresh water that floated on the typically cold, salty waters of the north Atlantic Ocean. Over the subsequent years, the anomaly drifted about the North Atlantic, first around the southern tip of Greenland, then off to the coast of Canada, then up and around, along the Gulf Stream to northern Europe. As it traveled, the freshwater pool acted as a cap, limiting the interaction between the air and the ocean.

According to Oceanus, the magazine of the Woods Hole Oceanographic Institution, “[t]he GSA acted as a sort of moving blanket, insulating different parts of the deep ocean from contact with the atmosphere as it moved around the gyre.” Similar events have happened in the decades that followed, and scientists have found that they can cause unusual temperature patterns for the United States and northern Europe, and may even affect fish populations.

Paper link.

Could Leakage from the Agulhas Current System Moderate Europe's Changed Climate?

South African Ocean Currents Could Stabilize Europe's Climate

One of the ocean currents which particularly interests oceanographers and climatologists is the Gulf Stream. This current, originating in the Gulf of Mexico, transports enormous amounts of warm tropical waters to the North Atlantic and is the cause of Europe's habitable climate. Climate predictions point to the fact that this will change in the future and affect especially the climate in countries of the Mediterranean region, with more dry spells. As global warming progresses, the North Atlantic will receive more precipitation and a greater amount of water from the melting of glaciers in Greenland, thus reducing the salinity of ocean water and weakening the Gulf Stream's effects.

The article published in Nature describes an alternative approach which suggests that flows from the Indian Ocean to the South Atlantic, near the tip of Africa, also are important in relation to future current systems in the North Atlantic.

The Agulhas Current, located in the southwest of the Indian Ocean, transports high density salt water to the southern tip of Africa, where part of it escapes to the South Atlantic, contributing to the strength of the global circulation of this ocean. The study describes how this inflow of salt water from the Indian Ocean can compensate the decrease in salinity in the North Atlantic and therefore stabilise the Gulf Stream and the climate in Europe. These processes have been simulated using computational climate models.

The article reviews information available until now and enumerates the steps which must be taken with the aim of carrying out a better assessment of the processes involved in this current system. To demonstrate the dynamics of the Agulhas Current, its sensitivity to climate change and the way it transmits its signals to the North Atlantic, researchers point out the need to combine long-term studies on temperature variation and salinity of the Agulhas Current, analyses on climate changes in the past and detailed computer simulation models.

Let's hope so our its going to be very uncomfy in Europe soon.