The phytoplankton community structure can reflect changes in the marine environment and help us understand the driving factors behind ecological evolution. The quantifying pigment concentration in phytoplankton is crucial for a comprehensive assessment of taxonomic classification and community structure.

Recently, a research team led by Prof. LI Xiaofeng from the Institute of Oceanology of the Chinese Academy of Sciences (IOCAS) has made progress in the inversion of global phytoplankton pigment concentrations using deep learning algorithms. Using satellite data, they developed a deep-learning-based model (DL-PPCE model) for estimating concentrations of 17 different phytoplankton pigments globally.

The study was published in Remote Sensing of Environment on May 19.

The model inputs include ocean color parameters, satellite-derived environmental parameters, and the slope of above-surface remote-sensing reflectance. The model was validated against high-performance liquid chromatography (HPLC) data and was advantageous for analyzing the phytoplankton community dynamics on a large spatiotemporal scale.

Using the established DL-PPCE model, the researchers conducted a time series analysis of global pigment concentrations retrieved by Moderate-resolution Imaging Spectroradiometer (MODIS) during the period of 2003-2021. They found that the prokaryotes-dominated area extended eastward from180°E to 150°W during the 2015/2016 El Nino event. From 2003 to 2021, prokaryotic abundance was positively correlated with El Nino intensity but negatively correlated with the quantity of the entire phytoplankton community.

Ocean color remote sensing enables the retrieval of phytoplankton absorption, which is directly linked to pigment concentration. "However, the simultaneous retrieval of multiple pigment concentrations globally is challenging due to optical property variability in seawater and the packaging effect on phytoplankton absorption," said LI Xiaolong, the first author of the study.

"In our study, we employ a novel approach to estimate global phytoplankton pigment concentrations," said Prof. LI, corresponding author of the study. "By avoiding assumptions about pigment absorption spectra and employing deep learning, we established non-linear relationships between remote sensing variables and phytoplankton pigment concentrations. This approach yielded high accuracy in estimating pigment concentrations."

The Breakthrough Listen Investigation for Periodic Spectral Signals (BLIPSS), led by Akshay Suresh, Cornell doctoral candidate in astronomy, is pioneering a search for periodic signals emanating from the core of our galaxy, the Milky Way. The research aims to detect repetitive patterns, a way to search for extraterrestrial intelligence (SETI) within our cosmic neighborhood. 

The researchers developed software based on a Fast Folding Algorithm (FFA), an efficient search method offering enhanced sensitivity to periodic sequences of narrow pulses. Their paper, “A 4–8 GHz Galactic Center Search for Periodic Technosignatures,” was published May 30 in The Astronomical Journal.

Pulsars -- rapidly rotating neutron stars that sweep beams of radio energy across the Earth -- are natural astrophysical objects that generate periodic signals but humans also use directed periodic transmissions for a variety of applications, including radar. Such signals would be a good way to get someone’s attention across interstellar space, standing out from the background of non-periodic signals, as well as using much less energy than a transmitter that is broadcasting continuously.

“BLIPSS is an example of cutting-edge software as a science multiplier for SETI,” said Suresh. “Our study introduces to SETI, for the first time, the Fast Folding Algorithm; our open-source software utilizes an FFA to crunch over 1.5 million time series for periodic signals in roughly 30 minutes.”

BLIPSS is a collaborative effort between Cornell, the SETI Institute, and Breakthrough Listen. The project significantly enhances the probability of capturing evidence of extraterrestrial technology by focusing on the central region of the Milky Way, known for its dense concentration of stars and potentially habitable exoplanets. The center of the Milky Way would also be an ideal place for aliens to place a beacon to contact large swaths of the Galaxy.

The team tested their algorithm on known pulsars and were able to detect periodic emissions1. Use simpler language: While the text is informative and technical, some of the language used may be difficult for the average reader to understand. To improve the effectiveness of the writing, it may be helpful to use simpler language to explain concepts and avoid jargon.

2. Provide more context: While the text provides some context, it may be helpful to provide more information on the significance of the research and its potential implications for the field of astronomy and the search for extraterrestrial life.

3. Include visuals: To make the text more engaging and easier to understand, it may be helpful to include visuals such as diagrams or illustrations to explain the concepts being discussed. This can help readers better understand the research and its potential implications. as expected. They then turned to a larger dataset of scans of the Galactic Center undertaken using the Breakthrough Listen instrument on the 100-meter Green Bank Telescope (GBT) in West Virginia. In contrast to pulsars, which emit across a wide swath of radio frequencies, BLIPSS looked for repeating signals in a narrower range of frequencies, covering less than one-tenth of the width of an average FM radio station.

“The combination of these relatively narrow bandwidths with periodic patterns could be indicative of deliberate technological activities of intelligent civilizations,” said co-author Steve Croft, Breakthrough Listen project scientist. “Breakthrough Listen captures huge volumes of data, and Akshay’s technique provides a new method to help us search that haystack for needles that could provide tantalizing evidence of advanced extraterrestrial life forms.”

“Until now, radio SETI has primarily dedicated its efforts to the search for continuous signals,” said co-author Vishal Gajjar, a SETI Institute astronomer. “Our study sheds light on the remarkable energy efficiency of a train of pulses as a means of interstellar communication across vast distances. Notably, this study marks the first-ever comprehensive endeavor to conduct in-depth searches for these signals.”

The rapid development of unexpected drought, called flash drought, can severely impact agricultural and ecological systems with ripple effects that extend even further. Researchers at the University of Oklahoma are assessing how our warming climate will affect the frequency of flash droughts and the risk to croplands globally. Jordan Christian, a postdoctoral researcher, is the lead author of the study.

“In this study, projected changes in flash drought frequency and cropland risk from flash drought are quantified using global climate model simulations,” Christian said. “We find that flash drought occurrence is expected to increase globally among all scenarios, with the sharpest increases seen in scenarios with higher radiative forcing and greater fossil fuel usage.” 

Radiative forcing describes the imbalance of radiation where more radiation enters Earth’s atmosphere than leaves it. Like burning fossil fuels, these activities are among the most significant contributors to climate warming. The changing climate is expected to increase severe weather events from storms, flash flooding, flash droughts, and more.

“Flash drought risk over cropland is expected to increase globally, with the largest increases projected across North America and Europe,” Christian said.

“CMIP6 models projected a 1.5 times increase in the annual risk of flash droughts over croplands across North America by 2100, from the 2015 baseline of a 32% yearly risk in 2015 to 49% in 2100, while Europe is expected to have the largest increase in the most extreme emissions scenario (32% to 53%), a 1.7 times increase in annual risk,” he said.

Jeffrey Basara, an associate professor in the School of Meteorology in the College of Atmospheric and Geographic Sciences and the School of Civil Engineering and Environmental Sciences in the Gallogly College of Engineering, is Christian’s faculty advisor and study co-author. Basara is the executive associate director of the hydrology and water security program and leads OU’s Climate, Hydrology, Ecosystems, and Weather research group. The researchers have been investigating ways to improve flash drought identification and prediction since 2017, with multiple papers published in journals.

“This study continues to emphasize that agricultural producers, both domestic and abroad, will face increasing risks associated with water availability due to the rapid development of drought. As a result, socioeconomic pressures associated with food production, including higher prices and social unrest, will also increase when crop losses occur due to flash drought,” Basara said.

New methods will allow for better tests of Einstein's general theory of relativity using LIGO data

Albert Einstein's general theory of relativity describes how the fabric of space and time, or spacetime, is curved in response to mass. Our sun, for example, warps space around us such that planet Earth rolls around the sun like a marble tossed into a funnel (Earth does not fall into the sun due to the Earth's sideways momentum). 

The theory, which was revolutionary at the time it was proposed in 1915, recast gravity as a curving of spacetime. As fundamental as this theory is to the very nature of space around us, physicists say it might not be the end of the story. Instead, they argue that theories of quantum gravity, which attempt to unify general relativity with quantum physics, hold secrets to how our universe works at the deepest levels.

One place to search for signatures of quantum gravity is in the mighty collisions between black holes, where gravity is at its most extreme. Black holes are the densest objects in the universe—their gravity is so strong that they squeeze objects falling into them into spaghetti-like noodles. When two black holes collide and merge into one larger body, they roil space-time around them, sending ripples called gravitational waves outward in all directions.

The National Science Foundation-funded LIGO, managed by Caltech and MIT, has been routinely detecting gravitational waves generated by black hole mergers since 2015 (its partner observatories, Virgo and KAGRA, joined the hunt in 2017 and 2020, respectively). So far, however, the general theory of relativity has passed test after test with no signs of breaking down.

Now, two new Caltech-led papers, in Physical Review X and Physical Review Letters, describe new methods for putting general relativity to even more stringent tests. By looking more closely at the structures of black holes, and the ripples in space-time they produce, scientists are seeking signs of small deviations from general relativity that would hint at the presence of quantum gravity.

"When two black holes merge to produce a bigger black hole, the final black hole rings like a bell," explains Yanbei Chen (Ph.D. '03), a professor of physics at Caltech and a co-author of both studies. "The quality of the ringing, or its timbre, may be different from the predictions of general relativity if certain theories of quantum gravity are correct. Our methods are designed to look for differences in the quality of this ringdown phase, such as the harmonics and overtones, for example."

The first paper, led by Caltech graduate student Dongjun Li, reports a new single equation to describe how black holes would ring within the framework of certain quantum gravity theories, or in what scientists refer to as the beyond-general-relativity regime.

The work builds upon a ground-breaking equation developed 50 years ago by Saul Teukolsky (Ph.D. '73), the Robinson Professor of Theoretical Astrophysics at Caltech. Teukolsky developed a complex equation to better understand how the ripples of space-time geometry propagate around black holes. In contrast to numerical relativity methods, in which supercomputers are required to simultaneously solve many differential equations about general relativity, the Teukolsky equation is much simpler to use and, as Li explains, provides direct physical insight into the problem.

"If one wants to solve all the Einstein equations of a black hole merger to accurately simulate it, they must turn to supercomputers," Li says. "Numerical relativity methods are incredibly important for accurately simulating black hole mergers, and they provide a crucial foundation for interpreting LIGO data. But it is extremely hard for physicists to draw intuitions directly from the numerical results. The Teukolsky equation gives us an intuitive look at what is going on in the ringdown phase."

Li was able to take Teukolsky's equation and adapt it for black holes in the beyond-general-relativity regime for the first time. "Our new equation allows us to model and understand gravitational waves propagating around black holes that are more exotic than Einstein predicted," he says.

The second paper, published in Physical Review Letters, led by Caltech graduate student Sizheng Ma, describes a new way to apply Li's equation to actual data acquired by LIGO and its partners in their next observational run. This data analysis approach uses a series of filters to remove features of a black hole's ringing predicted by general relativity so that potentially subtle, beyond-general-relativity signatures can be revealed.

"We can look for features described by Dongjun's equation in the data that LIGO, Virgo, and KAGRA will collect," Ma says. "Dongjun has found a way to translate a large set of complex equations into just one equation, and this is tremendously helpful. This equation is more efficient and easier to use than methods we used before." 

The two studies complement each other well, Li says. "I was initially worried that the signatures my equation predicts would be buried under the multiple overtones and harmonics; fortunately, Sizheng's filters can remove all these known features, which allows us to just focus on the differences," he says.

Chen added: "Working together, Li and Ma's findings can significantly boost our community's ability to probe gravity."