Linkages Among Dissolved Organic Matter Export, Dissolved Metabolites, and Associated Microbial Community Structure Response in the Northwestern Sargasso Sea on a Seasonal Scale.

Deep convective mixing of dissolved and suspended organic matter from the surface to depth can represent an important export pathway of the biological carbon pump. The seasonally oligotrophic Sargasso Sea experiences annual winter convective mixing to as deep as 300 m, providing a unique model system to examine dissolved organic matter (DOM) export and its subsequent compositional transformation by microbial oxidation. We analyzed biogeochemical and microbial parameters collected from the northwestern Sargasso Sea, including bulk dissolved organic carbon (DOC), total dissolved amino acids (TDAA), dissolved metabolites, bacterial abundance and production, and bacterial community structure, to assess the fate and compositional transformation of DOM by microbes on a seasonal time-scale in 2016-2017. DOM dynamics at the Bermuda Atlantic Time-series Study site followed a general annual trend of DOC accumulation in the surface during stratified periods followed by downward flux during winter convective mixing. Changes in the amino acid concentrations and compositions provide useful indices of diagenetic alteration of DOM. TDAA concentrations and degradation indices increased in the mesopelagic zone during mixing, indicating the export of a relatively less diagenetically altered (i.e., more labile) DOM. During periods of deep mixing, a unique subset of dissolved metabolites, such as amino acids, vitamins, and benzoic acids, was produced or lost. DOM export and compositional change were accompanied by mesopelagic bacterial growth and response of specific bacterial lineages in the SAR11, SAR202, and SAR86 clades, Acidimicrobiales, and Flavobacteria, during and shortly following deep mixing. Complementary DOM biogeochemistry and microbial measurements revealed seasonal changes in DOM composition and diagenetic state, highlighting microbial alteration of the quantity and quality of DOM in the ocean.

Management of Marfan Syndrome during pregnancy: A real world experience from a Joint Cardiac Obstetric Service.

BACKGROUND: Pregnancy in Marfan Syndrome (MFS) is associated with increased maternal risk of cardiovascular events. Given the maternal and genetic risks, pre-conception counselling is essential to facilitate informed choices. Multidisciplinary antenatal care with regular imaging is mandatory and best delivered through a Joint Cardiac Obstetric Service (JCOS). The aim of this study was to compare the care delivered in a JCOS against recognised international standards (European Society of Cardiology (ESC)). METHODS: Pregnancies in women with MFS from 2005 to 2015 were identified from our institutional database. Patient records were reviewed and practice assessed against pre-determined standards based on ESC guidelines. RESULTS: There were 23 pregnancies in 15 women with MFS. 13/23 (57%) occurred in women with aortic dilatation at baseline. There were 3 important maternal cardiac events (type A dissection; deterioration in left ventricular function; significant left ventricular and progressive aortic dilatation). Four women did not have access to expert pre-conception counselling. These women were all referred to the JCOS late in established pregnancy. Imaging was often delayed and only 7/23 cases (30%) met the standard for minimum frequency of echocardiographic surveillance. Only 12/23 (52%) had pre-conception imaging of the whole aorta with CT/MRI. Distal aortic dilatation was identified in 7/23 cases but none of these underwent further MRI evaluation during pregnancy. CONCLUSION: Despite having a dedicated JCOS, our data show that facilitating complete obstetric and cardiac care for this group remains challenging. Education of local care providers and timely referral for expert pre-conception counselling in a JCOS are key.

The contribution of heart disease to maternal mortality.

PURPOSE OF REVIEW: Heart disease is a leading cause of maternal death worldwide. In western countries, the principal causes of death from heart disease are myocardial infarction, cardiomyopathy and congenital heart disease, whereas in developing countries, rheumatic heart disease and its long-term consequences are more important. RECENT FINDINGS: There are few prospective studies upon which to base the management of these complex cases. However, best practice includes the assessment of women prepregnancy by a multidisciplinary team, with the aim of optimizing the clinical state, changing therapy to avoid teratogenic treatments and advising the patient and her relatives about the potential risks and possible complications that may arise. During pregnancy, the multidisciplinary team should define the level of care/surveillance required in each case. Some women may be safely looked after in a peripheral hospital, whereas others may need to be seen by the multidisciplinary team in the tertiary centre at regular intervals along with close echocardiographic monitoring. SUMMARY: The majority of women with preexisting heart disease can go through pregnancy safely, however, close attention to detail must be paid to avoid potential complications.

Effect of maternal heart disease on fetal growth.

OBJECTIVE: To estimate the effect of maternal heart disease on fetal growth and neonatal outcomes. METHODS: A retrospective cohort study of all women with congenital and acquired heart disease admitted at Chelsea and Westminster Hospital between 1994 and 2010 was performed. The women who delivered immediately before and immediately after each index pregnancy were used as controls. Data were obtained from medical and obstetric notes. Birth weight percentiles were calculated using a customized birth weight percentile program, and neonatal complications (preterm birth, perinatal mortality, and recurrence of congenital heart disease) were noted. RESULTS: Median birth weight percentile was significantly lower in the heart disease group (31) compared with the control group (49;P.001 Mann-Whitney U test [corrected].The rate of neonatal complications was significantly higher in the heart disease group (34% compared with 15%). Preterm birth occurred in 42 (13%) pregnancies, of which 67% were iatrogenic. Eighty-one (25%) newborns in the heart disease group were small for gestational age, and there were four stillbirths and four neonatal deaths (perinatal mortality rate 20 per 1,000). CONCLUSION: This cohort study suggests a significant reduction in fetal growth rates associated with maternal heart disease, which is also associated with preterm delivery and reduced birth weight. The presence of maternal cyanosis and a reduced cardiac output are the most significant predictors. LEVEL OF EVIDENCE: II.

Pregnancy in women with a systemic right ventricle after surgically and congenitally corrected transposition of the great arteries.

OBJECTIVE: To determine maternal and neonatal outcomes in women with a systemic right ventricle (RV). STUDY DESIGN: A retrospective (historical) cohort study of maternal and neonatal outcomes at a tertiary referral academic obstetric unit (Chelsea and Westminster Hospital, London). RESULTS: Nineteen pregnancies in 14 women with a systemic RV were compared with 76 controls. There were no maternal deaths. In the study group cardiac complications occurred in six (32%) pregnancies. Obstetric complications occurred in four (21%) case pregnancies, not significantly higher than in the control group. The rate of neonatal complication was significantly higher in the study population with neonatal complications in 12 (63%) case pregnancies compared with 13 (17%) control pregnancies. The median birthweight centile was 9 in the study population, significantly lower than the control population. CONCLUSIONS: Our cohort study demonstrates high maternal and neonatal morbidity and low birthweight in the presence of a systemic RV. Cardiac complications were more common in women with RV dysfunction and arrhythmias prior to pregnancy. Preconception counselling and tertiary care during pregnancy for these patients is highly advisable.

Cardiac disease in pregnancy.

PURPOSE OF REVIEW: The past 15 years have seen a five-fold increase in the incidence of acquired heart disease as a cause of maternal mortality in the UK, and advances in the surgical correction of congenital heart disease have enabled many more women to survive childhood and present at the antenatal clinic. This review updates the reader on these important conditions. RECENT FINDINGS: The major increased incidence of acute myocardial infarction during pregnancy has been attributed to an increasing proportion of older women having babies (risk 30-fold greater for women over 40 years compared with women under 20 years of age). The obesity epidemic is associated with increases in diabetes and hypertension. Percutaneous coronary intervention with stenting is the treatment of choice. Although aortopathies, cardiomyopathy and valvular heart disease present continuing problems, improvements in the management of pulmonary vascular disease (in particular, the use of sildenafil) have reduced mortality from this condition. Prophylaxis against endocarditis has been abandoned except for the highest risk cases. SUMMARY: Cardiac disease in pregnancy is of growing importance both in terms of numbers of women affected and mortality. Improvements in care have occurred particularly in relation to ischaemic heart disease and pulmonary hypotension.

Trajectory shifts in the Arctic and subarctic freshwater cycle.

Manifold changes in the freshwater cycle of high-latitude lands and oceans have been reported in the past few years. A synthesis of these changes in freshwater sources and in ocean freshwater storage illustrates the complementary and synoptic temporal pattern and magnitude of these changes over the past 50 years. Increasing river discharge anomalies and excess net precipitation on the ocean contributed approximately 20,000 cubic kilometers of fresh water to the Arctic and high-latitude North Atlantic oceans from lows in the 1960s to highs in the 1990s. Sea ice attrition provided another approximately 15,000 cubic kilometers, and glacial melt added approximately 2000 cubic kilometers. The sum of anomalous inputs from these freshwater sources matched the amount and rate at which fresh water accumulated in the North Atlantic during much of the period from 1965 through 1995. The changes in freshwater inputs and ocean storage occurred in conjunction with the amplifying North Atlantic Oscillation and rising air temperatures. Fresh water may now be accumulating in the Arctic Ocean and will likely be exported southward if and when the North Atlantic Oscillation enters into a new high phase.

Dilution of the northern North Atlantic Ocean in recent decades.

Declining salinities signify that large amounts of fresh water have been added to the northern North Atlantic Ocean since the mid-1960s. We estimate that the Nordic Seas and Subpolar Basins were diluted by an extra 19,000 +/- 5000 cubic kilometers of freshwater input between 1965 and 1995. Fully half of that additional fresh water-about 10,000 cubic kilometers-infiltrated the system in the late 1960s at an approximate rate of 2000 cubic kilometers per year. Patterns of freshwater accumulation observed in the Nordic Seas suggest a century time scale to reach freshening thresholds critical to that portion of the Atlantic meridional overturning circulation.

A change in the freshwater balance of the Atlantic Ocean over the past four decades.

The oceans are a global reservoir and redistribution agent for several important constituents of the Earth's climate system, among them heat, fresh water and carbon dioxide. Whereas these constituents are actively exchanged with the atmosphere, salt is a component that is approximately conserved in the ocean. The distribution of salinity in the ocean is widely measured, and can therefore be used to diagnose rates of surface freshwater fluxes, freshwater transport and local ocean mixing--important components of climate dynamics. Here we present a comparison of salinities on a long transect (50 degrees S to 60 degrees N) through the western basins of the Atlantic Ocean between the 1950s and the 1990s. We find systematic freshening at both poleward ends contrasted with large increases of salinity pervading the upper water column at low latitudes. Our results extend a growing body of evidence indicating that shifts in the oceanic distribution of fresh and saline waters are occurring worldwide in ways that suggest links to global warming and possible changes in the hydrologic cycle of the Earth.

Recent changes in the North Atlantic.

It has long been recognized that the Atlantic meridional overturning circulation (MOC) is potentially sensitive to greenhouse-gas and other climate forcing, and that changes in the MOC have the potential to cause abrupt climate change. However, the mechanisms remain poorly understood and our ability to detect these changes remains incomplete. Four main (interrelated) types of ocean change in particular are associated in the literature with greenhouse-gas forcing. These are: a slowing of MOC overturning rate; changes in northern seas which might effect a change in Atlantic overturning, including changes in the freshwater flux from the Arctic, and changes in the transport and/or hydrographic character of the northern overflows which ventilate the deep Atlantic; a change in the trans-ocean gradients of steric height (both zonal and meridional) which might accompany a change in the MOC; and an intensification of the global water cycle. Though as yet we have no direct measure of the freshwater flux passing from the Arctic to the Atlantic either via the Canadian Arctic Archipelago or along the East Greenland Shelf, and no direct measure yet of the Atlantic overturning rate, we examine a wide range of time-series from the existing hydrographic record for oceanic evidence of the other anticipated responses. Large amplitude and sustained changes are found (or indicated by proxy) over the past three to four decades in the southward transport of fresh waters along the Labrador shelf and slope, in the hydrography of the deep dense overflows from Nordic seas, in the transport of the eastern overflow through Faroe Bank Channel, and in the global hydrologic cycle. Though the type and scale of changes in ocean salinity are consistent with an amplification of the water cycle, we find no convincing evidence of any significant, concerted slowdown in the Atlantic overturning circulation.