ALBERT

Description: Highlights: • Lagrangian ocean analysis is a powerful way to analyse the output of ocean circulation models • We present a review of the Kinematic framework, available tools, and applications of Lagrangian ocean analysis • While there are unresolved questions, the framework is robust enough to be used widely in ocean modelling Abstract: Lagrangian analysis is a powerful way to analyse the output of ocean circulation models and other ocean velocity data such as from altimetry. In the Lagrangian approach, large sets of virtual particles are integrated within the three-dimensional, time-evolving velocity fields. Over several decades, a variety of tools and methods for this purpose have emerged. Here, we review the state of the art in the field of Lagrangian analysis of ocean velocity data, starting from a fundamental kinematic framework and with a focus on large-scale open ocean applications. Beyond the use of explicit velocity fields, we consider the influence of unresolved physics and dynamics on particle trajectories. We comprehensively list and discuss the tools currently available for tracking virtual particles. We then showcase some of the innovative applications of trajectory data, and conclude with some open questions and an outlook. The overall goal of this review paper is to reconcile some of the different techniques and methods in Lagrangian ocean analysis, while recognising the rich diversity of codes that have and continue to emerge, and the challenges of the coming age of petascale computing.

Description: Ten ODP sites drilled in a depth transect (2164–4775 m water depth) during Leg 172 recovered high-deposition rate (〉20 cm/kyr) sedimentary sections from sediment drifts in the western North Atlantic. For each site an age model covering the past 0.8–0.9 Ma has been developed. The time scales have a resolution of 10–20 kyr and are derived by tuning variations of estimated carbonate content to the orbital parameters precession and obliquity. Based on the similarity in the signature of proxy records and the spectral character of the time series, the sites are divided into two groups: precession cycles are better developed in carbonate records from a group of shallow sites (2164–2975 m water depth, Sites 1055–1058) while the deeper sites (2995–4775 m water depth, Sites 1060–1063) are characterized by higher spectral density in the obliquity band. The resulting time scales show excellent coherence with other dated carbonate and isotope records from low latitudes. Besides the typical Milankovitch cyclicity significant variance of the resulting carbonate time series is concentrated at millennial-scale changes with periods of about 12, 6, 4, 2.5, and 1.5 kyr. Comparisons of carbonate records from the Blake Bahama Outer Ridge and the Bermuda Rise reveal a remarkable similarity in the time and frequency domain indicating a basin-wide uniform sedimentation pattern during the last 0.9 Ma.

Description: Highlights: • Arctic sea ice extent and solid freshwater in 14 CORE-II models are inter-compared. • The models better represent the variability than the mean state. • The September ice extent trend is reasonably represented by the model ensemble mean. • The descending trend of ice thickness is underestimated compared to observations. • The models underestimate the reduction in solid freshwater content in recent years. Abstract: The Arctic Ocean simulated in fourteen global ocean-sea ice models in the framework of the Coordinated Ocean-ice Reference Experiments, phase II (CORE II) is analyzed. The focus is on the Arctic sea ice extent, the solid freshwater (FW) sources and solid freshwater content (FWC). Available observations are used for model evaluation. The variability of sea ice extent and solid FW budget is more consistently reproduced than their mean state in the models. The descending trend of September sea ice extent is well simulated in terms of the model ensemble mean. Models overestimating sea ice thickness tend to underestimate the descending trend of September sea ice extent. The models underestimate the observed sea ice thinning trend by a factor of two. When averaged on decadal time scales, the variation of Arctic solid FWC is contributed by those of both sea ice production and sea ice transport, which are out of phase in time. The solid FWC decreased in the recent decades, caused mainly by the reduction in sea ice thickness. The models did not simulate the acceleration of sea ice thickness decline, leading to an underestimation of solid FWC trend after 2000. The common model behavior, including the tendency to underestimate the trend of sea ice thickness and March sea ice extent, remains to be improved.

Description: Highlights: • Arctic liquid freshwater budget simulated in 14 CORE-II models is studied. • The models better represent the temporal variability than the mean state. • Multi-model mean (MMM) FW fluxes compare well with observations. • MMM FWC shows an upward trend in the recent years, with an underestimated rate. • FW flux interannual variability is more consistent where volume flux determines it. Abstract: The Arctic Ocean simulated in 14 global ocean-sea ice models in the framework of the Coordinated Ocean-ice Reference Experiments, phase II (CORE-II) is analyzed in this study. The focus is on the Arctic liquid freshwater (FW) sources and freshwater content (FWC). The models agree on the interannual variability of liquid FW transport at the gateways where the ocean volume transport determines the FW transport variability. The variation of liquid FWC is induced by both the surface FW flux (associated with sea ice production) and lateral liquid FW transport, which are in phase when averaged on decadal time scales. The liquid FWC shows an increase starting from the mid-1990s, caused by the reduction of both sea ice formation and liquid FW export, with the former being more significant in most of the models. The mean state of the FW budget is less consistently simulated than the temporal variability. The model ensemble means of liquid FW transport through the Arctic gateways compare well with observations. On average, the models have too high mean FWC, weaker upward trends of FWC in the recent decade than the observation, and low consistency in the temporal variation of FWC spatial distribution, which needs to be further explored for the purpose of model development.

Description: Dissolved free amino acids (DFAA) in seawater are a form of nitrogen (N) available for marine microbes. In oligotrophic environments where N-containing nutrients are the limiting factor for microbial growth, N nutrition from DFAA could be crucial, but as yet it is poorly resolved. Measurements of individual DFAA are challenging as concentrations are typically in the low nmol L− 1 range. Here we report modifications to methodology using o-phthaldialdehyde (OPA) derivatization and reversed phase high performance liquid chromatography (HPLC) that provide a 30-fold improvement in sensitivity enabling the detection of 15 amino acids in seawater with a limit of detection as low as 10 pmol L− 1 with accuracy and precision of better than 10%. This analytical methodology is now suitable for the challenging quantitation of DFAA in oligotrophic seawaters. The method was successfully applied to a suite of seawater samples collected on a cruise crossing the South Atlantic Ocean, where concentrations of DFAAs were generally low (sub nmol L− 1), revealing basin-scale features in the oceanographic distributions of DFAA. This unique dataset implies that DFAAs are an important component of the N cycle in both near-coastal and open oceans. Further calculations suggest that the proportions of organic N originating from DFAA sources were significant, contributing between 0.2 and 200% that of NH4 + and up to 77% that of total inorganic nitrogen in the upper 400 m in some regions of the transect.

Description: Highlights • The Southern Hemisphere mid-latitudes are characterised by obliquity and semi-precession cycles during the Mi-1 deglaciation • The obliquity variability is attributed to polar influence and the semi-precessional variability to tropical influence • Semi-precession cycles do not appear until 23.01 Ma, corresponding to the onset of Antarctic deglaciation • The interaction between polar and tropical influence is related to the position and strength of the westerly wind belt Abstract It is well-known from geologic archives that Pleistocene and Holocene climate is characterised by cyclical variation on a wide range of timescales, and that these cycles of variation interact in complex ways. However, it is rarely possible to reconstruct sub-precessional (〈 20 kyr) climate variations for periods predating the oldest ice-core records (c. 800 ka). Here we present an investigation of orbital to potentially sub-precessional cyclicity from an annually resolved lake sediment core dated to a 100-kyr period in the earliest Miocene (23.03–22.93 Ma) and spanning a period of major Antarctic deglaciation associated with the second half of the Mi-1 event. Principal component analysis (PCA) of sediment bulk density, magnetic susceptibility (MS), and CIELAB L* and b* with a resolution of ~10 years indicates two major environmental processes governing the physical properties records, which we interpret as changes in wind strength and changes in precipitation. Spectral analysis of the principal components indicates that both processes are strongly influenced by obliquity (41 kyr). We interpret this 41-kyr cycle in wind strength and precipitation as related to the changing position and strength of the Southern Hemisphere westerly winds. Precipitation is also influenced by an 11-kyr cycle. The 11-kyr periodicity is potentially related to orbital cyclicity, representing the equatorial semi-precessional maximum insolation cycle. This semi-precession cycle has been identified in a number of records from the Pleistocene and Holocene and has recently been suggested to indicate that insolation in low-latitude regions may be an important driver of millennial-scale climate response to orbital forcing (Feretti et al., 2015). This is the first time this cycle has been identified in a mid-latitude Southern Hemisphere climate archive, as well as the first identification in pre-Pleistocene records. The 11-kyr cycle appears at around 23.01 Ma, which coincides with the initiation of a major phase of Antarctic deglaciation, and strengthens during the subsequent period of rapid ice decay. This pattern suggests that the westerly winds may have expanded north of 50°S at the height of Mi-1, excluding tropical influence from the Foulden Maar site, and subsequently contracted polewards in tandem with warming deep-sea temperatures and Antarctic deglaciation, allowing the advection of tropical waters further south.

Description: Whilst Herpesviridae, which infect higher vertebrates, actively influence host immune responses to ensure viral replication, it is mostly unknown if Alloherpesviridae, which infect lower vertebrates, possess similar abilities. An important antiviral response is clearance of infected cells via apoptosis, which in mammals influences the outcome of infection. Here, we utilise common carp infected with CyHV-3 to determine the effect on the expression of genes encoding apoptosis-related proteins (p53, Caspase 9, Apaf-1, IAP, iNOS) in the pronephros, spleen and gills. The influence of CyHV-3 on CCB cells was also studied and compared to SVCV (a rhabdovirus) which induces apoptosis in carp cell lines. Although CyHV-3 induced iNOS expression in vivo, significant induction of the genetic apoptosis pathway was only seen in the pronephros. In vitro CyHV-3 did not induce apoptosis or apoptosis-related expression whilst SVCV did stimulate apoptosis. This suggests that CyHV-3 possesses mechanisms similar to herpesviruses of higher vertebrates to inhibit the antiviral apoptotic process.

Description: In the present work responses of carp (Cyprinus carpio) head kidney-derived neutrophils to the blood parasite T. borreli, and the consequences of these responses for parasite survival and other host response mechanisms, were studied. In co-cultures of head kidney leucocytes (HKL) with viable and lysed T. borreli a prominent shape change of neutrophilic granulocytes towards increased size and complexity was observed. In addition, the longevity of neutrophils in vitro was prolonged in the presence of T. borreli antigens. In these cultures, neutrophils also exhibited an increased phagocytosis activity. An up regulation of the production of nitric oxide (NO) and reactive oxygen species (ROS) was observed in T. borreli- and mitogen-stimulated HKL cultures. However, addition of live, fluorescence-labelledT. borreli to previously stimulated HKL cultures, revealed neither killing nor phagocytosis of the parasite by activated neutrophils. Moreover, viable T. borreli, when added to HKL cultures of infected carp, reduced their phagocytosis activity and NO production. Supernatants of co-cultures between T. borreli and HKL also contained mediators, which suppressed a mitogen-induced proliferative response of peripheral blood leucocytes (PBL) in vitro. Thus, while T. borreli itself appeared not to be sensitive to responses of activated neutrophils, the flagellates interferes with the production of immunomodulatory signals of these cells, probably resulting in a partial immunosuppression, which may favour the parasite development in vivo.

Description: This paper is an observational study of small-scale coherent eddies in the Labrador Sea, a region of dense water formation thought to be of considerable importance to the North Atlantic overturning circulation. Numerical studies of deep convection emphasize coherent eddies as a mechanism for the lateral transport of heat, yet their small size has hindered observational progress. A large part of this paper is therefore devoted to developing new methods for identifying and describing coherent eddies in two observational platforms, current meter moorings and satellite altimetry. Details of the current and water mass structure of individual eddy events, as they are swept past by an advecting flow, can then be extracted from the mooring data. A transition is seen during mid-1997, with long-lived boundary current eddies dominating the central Labrador Sea year-round after this time, and convectively formed eddies similar to those seen in deep convection modeling studies apparent prior to this time. The TOPEX / Poseidon altimeter covers the Labrador Sea with a loose “net” of observations, through which coherent eddies can seem to appear and disappear. By concentrating on locating and describing anomalous events in individual altimeter tracks, a portrait of the spatial and temporal variability of the underlying eddy field can be constructed. The altimeter results reveal an annual “pulsation” of energy and of coherent eddies originating during the late fall at a particular location in the boundary current, pinpointing the time and place of the boundary current-type eddy formation. The interannual variability seen at the mooring is reproduced, but the mooring site is found to be within a localized region of greatly enhanced eddy activity. Notably lacking in both the annual cycle and interannual variability is a clear relationship between the eddies or eddy energy and the intensity of wintertime cooling. These eddy observations, as well as hydrographic evidence, suggest an active role for boundary current dynamics in shaping the energetics and water mass properties of the interior region.