Onset of coupled atmosphere-ocean oxygenation 2.3 billion years ago.

The initial rise of molecular oxygen (O2) shortly after the Archaean-Proterozoic transition 2.5 billion years ago was more complex than the single step-change once envisioned. Sulfur mass-independent fractionation records suggest that the rise of atmospheric O2 was oscillatory, with multiple returns to an anoxic state until perhaps 2.2 billion years ago1-3. Yet few constraints exist for contemporaneous marine oxygenation dynamics, precluding a holistic understanding of planetary oxygenation. Here we report thallium (Tl) isotope ratio and redox-sensitive element data for marine shales from the Transvaal Supergroup, South Africa. Synchronous with sulfur isotope evidence of atmospheric oxygenation in the same shales3, we found lower authigenic 205Tl/203Tl ratios indicative of widespread manganese oxide burial on an oxygenated seafloor and higher redox-sensitive element abundances consistent with expanded oxygenated waters. Both signatures disappear when the sulfur isotope data indicate a brief return to an anoxic atmospheric state. Our data connect recently identified atmospheric O2 dynamics on early Earth with the marine realm, marking an important turning point in Earth's redox history away from heterogeneous and highly localized 'oasis'-style oxygenation.

A well-oxygenated eastern tropical Pacific during the warm Miocene.

The oxygen content of the oceans is susceptible to climate change and has declined in recent decades1, with the largest effect in oxygen-deficient zones (ODZs)2, that is, mid-depth ocean regions with oxygen concentrations <5 µmol kg-1 (ref. 3). Earth-system-model simulations of climate warming predict that ODZs will expand until at least 2100. The response on timescales of hundreds to thousands of years, however, remains uncertain3-5. Here we investigate changes in the response of ocean oxygenation during the warmer-than-present Miocene Climatic Optimum (MCO; 17.0-14.8 million years ago (Ma)). Our planktic foraminifera I/Ca and δ15N data, palaeoceanographic proxies sensitive to ODZ extent and intensity, indicate that dissolved-oxygen concentrations in the eastern tropical Pacific (ETP) exceeded 100 µmol kg-1 during the MCO. Paired Mg/Ca-derived temperature data suggest that an ODZ developed in response to an increased west-to-east temperature gradient and shoaling of the ETP thermocline. Our records align with model simulations of data from recent decades to centuries6,7, suggesting that weaker equatorial Pacific trade winds during warm periods may lead to decreased upwelling in the ETP, causing equatorial productivity and subsurface oxygen demand to be less concentrated in the east. These findings shed light on how warm-climate states such as during the MCO may affect ocean oxygenation. If the MCO is considered as a possible analogue for future warming, our findings seem to support models suggesting that the recent deoxygenation trend and expansion of the ETP ODZ may eventually reverse3,4.

Uncovering the Ediacaran phosphorus cycle.

Phosphorus is a limiting nutrient that is thought to control oceanic oxygen levels to a large extent1-3. A possible increase in marine phosphorus concentrations during the Ediacaran Period (about 635-539 million years ago) has been proposed as a driver for increasing oxygen levels4-6. However, little is known about the nature and evolution of phosphorus cycling during this time4. Here we use carbonate-associated phosphate (CAP) from six globally distributed sections to reconstruct oceanic phosphorus concentrations during a large negative carbon-isotope excursion-the Shuram excursion (SE)-which co-occurred with global oceanic oxygenation7-9. Our data suggest pulsed increases in oceanic phosphorus concentrations during the falling and rising limbs of the SE. Using a quantitative biogeochemical model, we propose that this observation could be explained by carbon dioxide and phosphorus release from marine organic-matter oxidation primarily by sulfate, with further phosphorus release from carbon-dioxide-driven weathering on land. Collectively, this may have resulted in elevated organic-pyrite burial and ocean oxygenation. Our CAP data also seem to suggest equivalent oceanic phosphorus concentrations under maximum and minimum extents of ocean anoxia across the SE. This observation may reflect decoupled phosphorus and ocean anoxia cycles, as opposed to their coupled nature in the modern ocean. Our findings point to external stimuli such as sulfate weathering rather than internal oceanic phosphorus-oxygen cycling alone as a possible control on oceanic oxygenation in the Ediacaran. In turn, this may help explain the prolonged rise of atmospheric oxygen levels.

A 200-million-year delay in permanent atmospheric oxygenation.

The rise of atmospheric oxygen fundamentally changed the chemistry of surficial environments and the nature of Earth's habitability1. Early atmospheric oxygenation occurred over a protracted period of extreme climatic instability marked by multiple global glaciations2,3, with the initial rise of oxygen concentration to above 10-5 of the present atmospheric level constrained to about 2.43 billion years ago4,5. Subsequent fluctuations in atmospheric oxygen levels have, however, been reported to have occurred until about 2.32 billion years ago4, which represents the estimated timing of irreversible oxygenation of the atmosphere6,7. Here we report a high-resolution reconstruction of atmospheric and local oceanic redox conditions across the final two glaciations of the early Palaeoproterozoic era, as documented by marine sediments from the Transvaal Supergroup, South Africa. Using multiple sulfur isotope and iron-sulfur-carbon systematics, we demonstrate continued oscillations in atmospheric oxygen levels after about 2.32 billion years ago that are linked to major perturbations in ocean redox chemistry and climate. Oxygen levels thus fluctuated across the threshold of 10-5 of the present atmospheric level for about 200 million years, with permanent atmospheric oxygenation finally arriving with the Lomagundi carbon isotope excursion at about 2.22 billion years ago, some 100 million years later than currently estimated.

[The Road to Discovery of the Pulmonary Gas Exchange - From the "Phlogiston-" to the "Oxygen Theory"]. / Der Weg zur Entdeckung des pulmonalen Gasaustausches.

The discovery of oxygen and pulmonary gas exchange was a major advancement in our understanding of breathing. For centuries it was believed that the lungs were primarily necessary to cool the heart or to "refine" the blood. Richard Lower (1631-1691) observed that the blood had a different colour before and after passage through the lung. His assumption was that breathing must have been added a special substance to the blood. Georg Ernst Stahl (1660-1734) formulated a fire substance "phlogiston" (phlox = flame) with his phlogiston theory. He postulated that phlogiston is contained in all combustible substances and escapes when burned. John Mayow (1641-1679) recognised that about one fifth of the breathing gas is important for the breathing process. He called the gas "spiritus nitro aerius". Oxygen was first discovered in the early 1770 s by the Swedish-German pharmacist Carl Wilhelm Scheele (1742-1786) and the English chemist Joseph Priestley (1733-1804) - independently of each other. Antoine-Laurent Lavoisier (1743-1794) recognised oxygen as element and for the first time described the oxidation process accurately.

A tribute to Robert John Porra (august 7, 1931-may 16, 2019).

Robert John Porra (7.8.1931-16.5.2019) is probably best known for his substantial practical contributions to plant physiology and photosynthesis by addressing the problems of both the accurate spectroscopic estimation and the extractability of chlorophylls in many organisms. Physiological data and global productivity estimates, in particular of marine primary productivity, are often quoted on a chlorophyll basis. He also made his impact by work on all stages of tetrapyrrole biosynthesis: he proved the C5 pathway to chlorophylls, detected an alternative route to protoporphyrin in anaerobes and the different origin of the oxygen atoms in anaerobes and aerobes. A brief review of his work is supplemented by personal memories of the authors.

The rise of oxygen in Earth's early ocean and atmosphere.

The rapid increase of carbon dioxide concentration in Earth's modern atmosphere is a matter of major concern. But for the atmosphere of roughly two-and-half billion years ago, interest centres on a different gas: free oxygen (O2) spawned by early biological production. The initial increase of O2 in the atmosphere, its delayed build-up in the ocean, its increase to near-modern levels in the sea and air two billion years later, and its cause-and-effect relationship with life are among the most compelling stories in Earth's history.

Thomas John Wydrzynski (8 July 1947-16 March 2018).

With this Tribute, we remember and honor Thomas John (Tom) Wydrzynski. Tom was a highly innovative, independent and committed researcher, who had, early in his career, defined his life-long research goal. He was committed to understand how Photosystem II produces molecular oxygen from water, using the energy of sunlight, and to apply this knowledge towards making artificial systems. In this tribute, we summarize his research journey, which involved working on 'soft money' in several laboratories around the world for many years, as well as his research achievements. We also reflect upon his approach to life, science and student supervision, as we perceive it. Tom was not only a thoughtful scientist that inspired many to enter this field of research, but also a wonderful supervisor and friend, who is deeply missed (see footnote*).

William E. Vidaver (1921-2017): an innovator, enthusiastic scientist, inspiring teacher and a wonderful friend.

William (Bill) E. Vidaver (February 2, 1921-August 31, 2017), who did his Ph.D. with Laurence (Larry) R. Blinks at Stanford (1964) and a postdoc with C. Stacy French (1965), taught and did research at Simon Fraser University (SFU) for almost 30 years. Here he published over 80 papers in photosynthesis-related areas co-authored by his graduate students, postdocs, visiting professors and SFU colleagues. He developed a unique high-pressure cuvette for the study of oxygen exchange and studied high-pressure effects in photosynthesis. Ulrich (Uli) Schreiber, as a postdoctoral fellow from Germany, introduced measurements on chlorophyll (Chl) a fluorescence to Bill's lab, leading to the discovery of reversible inhibition of excitation energy transfer between photosynthetic pigments and of a pivotal role of O2 in the oxidation of the electron transport chain between Photosystem II (PS II) and PS I. Bill's and Uli's work led to a patent of a portable chlorophyll fluorometer, the first available commercially, which was later modified to measure whole plantlets. The latter was used in pioneering measurement of the health of forest and crop plants undergoing in vitro clonal micropropagation. With several other researchers (including Doug Bruce, the late Radovan Popovic, and Sarah Swenson), he localized the quenching site of O2 and showed a dampening effect on measurements of the four-step process of O2 production by endogenous oxygen uptake. Bill is remembered as a hard-working but fun-loving person with a keen mind and strong sense of social justice.

Intraabdominal Surgery and Anesthesia Management.

Inspired Oxygenation in Surgical Patients During General Anesthesia With Controlled Ventilation: A Concept of Atelectasis. By Bendixen HH, Hedley-Whyte J, and Laver MB. New Engl J Med 1963; 269:991-996. Reprinted with permission. ABSTRACT: The purpose of this study was to determine if the pattern of ventilation, by itself, influences oxygenation during anesthesia and surgery and examine the hypothesis that progressive pulmonary atelectasis may occur during constant ventilation whenever periodic hyperventilation is lacking, but is reversible by passive hyperinflation of the lungs. Eighteen surgical patients, ranging in age from 24 to 87 yr, without known pulmonary disease, were studied during intraabdominal procedures and one radical mastectomy. Although ventilation remained constant, changes occurred in arterial oxygen tension and in total pulmonary compliance, with an average fall of 22% in oxygen tension and 15% in total pulmonary compliance. This fall in oxygen tension supports the hypothesis that progressive mechanical atelectasis may lead to increased venous admixture to arterial blood. The influence of the ventilator pattern on atelectasis and shunting is further illustrated by the reversibility of the fall in oxygen tension that follows hyperinflation. A relation between the degree of ventilation and the magnitude of fall in arterial oxygen tension was found, where large tidal volumes appear to protect against falls in oxygen tension, while shallow tidal volumes lead to atelectasis and increased shunting with impaired oxygenation.

The Most Important Discovery of Science.

Oxygen has often been called the most important discovery of science. I disagree. Over five centuries, reports by six scientists told of something in air we animals all need. Three reported how to generate it. It acquired many names, finally oxygen. After 8 years of studying it, Lavoisier still couldn't understand its nature. No special date and no scientist should get credit for discovering oxygen. Henry Cavendish discovered how to make inflammable air (H2). When burned, it made water. This was called impossible because water was assumed to be an element. When Lavoisier repeated the Cavendish test on June 24, 1783, he realized it demolished two theories, phlogiston and water as an element, a Kuhnian paradigm shift that finally unlocked his great revolution of chemistry.

ISOTT from the Beginning: A Tribute to Our Deceased Members (Icons).

ISOTT was founded by Drs. Duane F. Bruley and Haim I. Bicher in the state of South Carolina, USA in 1973. The symposium was jointly held at Clemson University (Clemson, SC, USA) and the Medical College of South Carolina (Charleston, SC, USA), which are geographically located 260 miles apart. This venue resulted from Dr. Bruley's (Clemson University) wish to have a meeting on Oxygen Transport to Tissue and with it to honor the research collaboration between the two universities and Dr. Melvin H. Knisely's accomplishments on studies regarding "blood sludging" in the microcirculation. Because of the unexpected large response to the symposium, Drs. Bruley and Bicher decided to found an international society at this meeting (ISOTT). The purpose of this paper is to summarize the formalization of ISOTT and to honor important contributors to the society who have since passed away. The authors did their best to include a brief overview of our past icons who have excelled in leadership as well as science/engineering, and apologize if someone has been mistakenly left out or if data is inaccurate or incomplete.

Proterozoic ocean redox and biogeochemical stasis.

The partial pressure of oxygen in Earth's atmosphere has increased dramatically through time, and this increase is thought to have occurred in two rapid steps at both ends of the Proterozoic Eon (∼2.5-0.543 Ga). However, the trajectory and mechanisms of Earth's oxygenation are still poorly constrained, and little is known regarding attendant changes in ocean ventilation and seafloor redox. We have a particularly poor understanding of ocean chemistry during the mid-Proterozoic (∼1.8-0.8 Ga). Given the coupling between redox-sensitive trace element cycles and planktonic productivity, various models for mid-Proterozoic ocean chemistry imply different effects on the biogeochemical cycling of major and trace nutrients, with potential ecological constraints on emerging eukaryotic life. Here, we exploit the differing redox behavior of molybdenum and chromium to provide constraints on seafloor redox evolution by coupling a large database of sedimentary metal enrichments to a mass balance model that includes spatially variant metal burial rates. We find that the metal enrichment record implies a Proterozoic deep ocean characterized by pervasive anoxia relative to the Phanerozoic (at least ∼30-40% of modern seafloor area) but a relatively small extent of euxinic (anoxic and sulfidic) seafloor (less than ∼1-10% of modern seafloor area). Our model suggests that the oceanic Mo reservoir is extremely sensitive to perturbations in the extent of sulfidic seafloor and that the record of Mo and chromium enrichments through time is consistent with the possibility of a Mo-N colimited marine biosphere during many periods of Earth's history.

Eight sages over five centuries share oxygen's discovery.

During the last century, historians have discovered that between the 13th and 18th centuries, at least six sages discovered that the air we breathe contains something that we need and use. Ibn al-Nafis (1213-1288) in Cairo and Michael Servetus (1511-1553) in France accurately described the pulmonary circulation and its effect on blood color. Michael Sendivogius (1566-1636) in Poland called a part of air "the food of life" and identified it as the gas made by heating saltpetre. John Mayow (1641-1679) in Oxford found that one-fifth of air was a special gas he called "spiritus nitro aereus." Carl Wilhelm Scheele (1742-1786) in Uppsala generated a gas he named "fire air" by heating several metal calcs. He asked Lavoisier how it fit the phlogiston theory. Lavoisier never answered. In 1744, Joseph Priestley (1733-1804) in England discovered how to make part of air by heating red calc of mercury. He found it brightened a flame and supported life in a mouse in a sealed bottle. He called it "dephlogisticated air." He published and personally told Lavoisier and other chemists about it. Lavoisier never thanked him. After 9 years of generating and studying its chemistry, he couldn't understand whether it was a new element. He still named it "principe oxigene." He was still not able to disprove phlogiston. Henry Cavendish (1731-1810) made an inflammable gas in 1766. He and Priestley noted that its flame made a dew. Cavendish proved the dew was pure water and published this in 1778, but all scientists called it impossible to make water, an element. In 1783, on June 24th, Lavoisier was urged to try it, and, when water appeared, he realized that water was not an element but a compound of two gases, proving that oxygen was an element. He then demolished phlogiston and began the new chemistry revolution.

Carl Wilhelm Scheele, the discoverer of oxygen, and a very productive chemist.

Carl Wilhelm Scheele (1742-1786) has an important place in the history of the discovery of respiratory gases because he was undoubtedly the first person to prepare oxygen and describe some of its properties. Despite this, his contributions have often been overshadowed by those of Joseph Priestley and Antoine Lavoisier, who also played critical roles in preparing the gas and understanding its nature. Sadly, Scheele was slow to publish his discovery and therefore Priestley is rightly recognized as the first person to report the preparation of oxygen. This being said, the thinking of both Scheele and Priestley was dominated by the phlogiston theory, and it was left to Lavoisier to elucidate the true nature of oxygen. In addition to his work on oxygen, Scheele was enormously productive in other areas of chemistry. Arguably he discovered seven new elements and many other compounds. However, he kept a low profile during his life as a pharmacist, and he did not have strong links with contemporary prestigious institutions such as the Royal Society in England or the French Académie des Sciences. He was elected to the Royal Swedish Academy of Science but only attended one meeting. Partly as a result, he remains a somewhat nebulous figure despite the critical contribution he made to the history of respiratory gases and his extensive researches in other areas of chemistry. His death at the age of 43 may have been hastened by his habit of tasting the chemicals that he worked on.

Joseph Priestley, oxygen, and the enlightenment.

Joseph Priestley (1733­1804) was the first person to report the discovery of oxygen and describe some of its extraordinary properties. As such he merits a special place in the history of respiratory physiology. In addition his descriptions in elegant 18th-century English were particularly arresting, and rereading them never fails to give a special pleasure. The gas was actually first prepared by Scheele (1742­1786) but his report was delayed. Lavoisier (1743­1794) repeated Priestley's initial experiment and went on to describe the true nature of oxygen that had eluded Priestley, who never abandoned the erroneous phlogiston theory. In addition to oxygen, Priestley isolated and characterized seven other gases. However, most of his writings were in theology because he was a conscientious clergyman all his life. Priestley was a product of the Enlightenment and argued that all beliefs should be able to stand the scientific scrutiny of experimental investigations. As a result his extreme liberal views were severely criticized by the established Church of England. In addition he was a supporter of both the French and American Revolutions. Ultimately his political and religious attitudes provoked a riot during which his home and his scientific equipment were destroyed. He therefore emigrated to America in 1794 where his friends included Thomas Jefferson and Benjamin Franklin. He settled in Northumberland, Pennsylvania although his scientific work never recovered from his forced departure. But the descriptions of his experiments with oxygen will always remain a high point in the history of respiratory physiology.

Stories and photographs of William A. Arnold (1904-2001), a pioneer of photosynthesis and a wonderful friend.

William A. Arnold discovered many phenomena in photosynthesis. In 1932, together with Robert Emerson, he provided the first experimental data that led to the concept of a large antenna and a few reaction centers (photosynthetic unit); in 1935, he obtained the minimum quantum requirement of 8-10 for the evolution of one O2 molecule; in 1951, together with Bernard L. Strehler, he discovered delayed fluorescence (also known as delayed light emission) in photosynthetic systems; and in 1956, together with Helen Sherwood, he discovered thermoluminescence in plants. He is also known for providing a solid-state picture of photosynthesis. Much has been written about him and his research, including many articles in a special issue of Photosynthesis Research (Govindjee et al. (eds.) 1996); and a biography of Arnold, by Govindjee and Srivastava (William Archibald Arnold (1904-2001), 2014), in the Biographical Memoirs of the US National Academy of Sciences, (Washington, DC). Our article here offers a glimpse into the everyday life, through stories and photographs, of this remarkable scientist.

The controversy over the minimum quantum requirement for oxygen evolution.

During the early- to mid-twentieth century, a bitter controversy raged among researchers on photosynthesis regarding the minimum number of light quanta required for the evolution of one molecule of oxygen. From 1923 until his death in 1970, Otto Warburg insisted that this value was about three or four quanta. Beginning in the late 1930s, Robert Emerson and others on the opposing side consistently obtained a value of 8-12 quanta. Warburg changed the protocols of his experiments, sometimes in unexplained ways, yet he almost always arrived at a value of four or less, except eight in carbonate/bicarbonate buffer, which he dismissed as "unphysiological". This paper is largely an abbreviated form of the detailed story on the minimum quantum requirement of photosynthesis, as told by Nickelsen and Govindjee (The maximum quantum yield controversy: Otto Warburg and the "Midwest-Gang", 2011); we provide here a scientific thread, leaving out the voluminous private correspondence among the principal players that Nickelsen and Govindjee (2011) examined in conjunction with their analysis of the principals' published papers. We explore the development and course of the controversy and the ultimate resolution in favor of Emerson's result as the phenomenon of the two-light-reaction, two-pigment-system scheme of photosynthesis came to be understood. In addition, we include a brief discussion of the discovery by Otto Warburg of the requirement for bicarbonate in the Hill reaction.

Crediting six discoverers of oxygen.

Recent events have called long-overdue attention to one of the first investigators to discover the roles of something in air changing the color of the pulmonary blood flowing through the lung.