Float Data Research Articles

A seasonal dipolar eddy near Ras Al Hamra (Sea of Oman)

Trajectories and hydrological data from two Argo floats indicate that warm and salty water at 200–300-m depths was ejected from the coast of Oman, near Ras al Hamra, in spring 2008, 2011, and 2012. This warm and salty water, Persian Gulf Water (PGW), once ejected from the coast, recirculated cyclonically in the western Sea of Oman, but also flowed eastward along the Iranian and Pakistani coasts. There, it was expelled seaward by mesoscale eddies as shown by other float data. Seasonal maps of salinity were computed from all available Argo floats; they showed that, in spring, PGW is present in the middle and north of the Sea of Oman, contrary to fall, when the salinity maxima lie southeast of Ras al Hadd. The ejection of PGW from Ras al Hamra is related here to the influence of a mesoscale dipolar eddy which often appears near this cape in spring. The time-averaged and empirical orthogonal functions of altimetric maps over 11 years for this season confirm the frequent presence and the persistence of this feature. From surface currents and hydrology, deep currents were computed via thermal wind balance, and the associated shear and strain fields were obtained. This deformation field is intense near Ras al Hamra, with an offshore direction. This flow structure associated with the mesoscale dipole explains PGW ejection from the coast. This observation suggests that PGW distribution in the Northern Arabian Sea can be strongly influenced by seasonal mesoscale eddies.

Geostrophic meridional transport in tropical Northwest Pacific based on Argo profiles

Absolute geostrophic currents in the North Pacific Ocean were calculated using P-vector method from newly gridded Argo profiling float data collected during 2004-2009. The meridional volume transport of geostrophic currents differed significantly from the classical Sverdrup balance, with differences of 10x10(6)-20x10(6)m(3)/s in the interior tropical Northwest Pacific Ocean. Analyses showed that errors of wind stress estimation could not explain all of the differences. The largest differences were found in the areas immediately north and south of the bifurcation latitude of the North Equatorial Current west of the dateline, and in the recirculation area of the Kuroshio and its extension, where nonlinear eddy activities were robust. Comparison of the geostrophic meridional transport and the wind-driven Sverdrup meridional transport in a high-resolution OFES simulation showed that nonlinear effects of the ocean circulation were the most likely reason for the differences. It is therefore suggested that the linear, steady wind-driven dynamics of the Sverdrup theory cannot completely explain the meridional transport of the interior circulation of the tropical Northwest Pacific Ocean.

The impact of meso-scale eddies on the Subtropical Mode Water in the western North Pacific

Based on the temperature and salinity from the Argo profiling floats and altimeter-derived geostrophic velocity anomaly (GVA) data in the western North Pacific during 2002–2011, the North Pacific Subtropical Mode Water (NPSTMW) distribution is investigated and cyclonic and anti-cyclonic eddies (CEs and AEs) are constructed to study the influence of their vertical structures on maintaining NPSTMW. Combining eddies identified by the GVA data and Argo profiling float data, it is found that the average NPSTMW thickness of AEs is about 60 dbar, which is thicker than that of CEs. The NPSTMW thicker than 150 dbar in AEs accounts for 18%, whereas that in CEs accounts for only 1%. About 3377 (3517) profiles, which located within one diameter of the nearest CEs (AEs) are used to construct the CE (AE). The composite AE traps low-PV water in the center and with a convex shape in the vertical section. The ‘trapped depth’ of the composite CE (AE) is 300 m (550 m) where the rotational velocity exceeds the transitional velocity. The present study suggests that the anticyclonic eddies are not only likely to form larger amounts of NPSTMW, but also trap more NPSTMW than cyclonic eddies.

Analisis Hubungan Suhu Permukaan Laut, Klorofil-a Data Satelit Modis Dan Sub-surface Temperature Data Argo Float Terhadap Hasil Tangkapan Tuna Di Samudera Hindia

Tuna is a large pelagic fish that has three characters. First, most of Tuna were found in upwelling and sea water front area. Second, Tuna have a migratory instinct to locate abundant source of food area. Third, each species of Tuna has sub-surface temperature preference The research used explorative method and the sampling method used purposive sampling. Data used in the research are sea surface temperature, chlorophyll-a from the MODIS satellite data and sub-surface temperature from the ARGO Float data. The result has shown that the highest Tuna catch occurs on the east season except for southern bluefin Tuna which was only caught on the west season. The upwelling phenomenon was detected on the west season and the sea water front phenomenon was detected on the east season. Analysis of single and multiple correlation between sub surface temperature and Tuna catch has shown high correlation with the coefficient correlation value is above 0.5 for both seasons. Based on the research, yellowfin Tuna has temperature range of 21 – 27 ⁰ C in the depth of 80 m – 100 m, bigeye Tuna is 10 – 23 ⁰ C in the depth of 150 m, albacore is 11 – 19 ⁰ C in the depth of 150 m and southern bluefin Tuna is 12 – 16 ⁰ C in the depth of 200 m.

Variation Features of the Mindanao Eddy from Argo Data

Based on monthly mean Argo profiler float data from 2004 to 2008 and monthly mean sea surface height and current velocity data from the Simple Ocean Data Assimilation (SODA) reanalysis for the period 1958–2007, the three-dimensional structure of the Mindanao Eddy (ME), its seasonal and interannual variability, and its impact on the thermohaline structure are analyzed. In addition, the displacement of the ME centre and its relation to ocean circulations are also discussed. The results showed that the ME spreads vertically from about 600 db depth upward to about 40 db depth. In addition to its strong seasonal variation, the strength of the ME displays strong interannual variability resulting from the interannual variability in the North Equatorial Current (NEC), the North Equatorial Counter Current (NECC) and the Mindanao Current (MC). The meridional movement of the centre of the ME has strong seasonal and interannual variability, and the zonal movement has a strong seasonal variation. The meridional movement is associated with the meridional displacement of the interface between the NECC and the NEC, whereas the zonal movement is associated with the zonal displacement of the interface between the MC and the northward branch of the NECC. The ME variability can greatly affect the pattern of the thermohaline structure in the local upper ocean. When the eddy is strong, the cold and low salinity water within it moves vigorously upward from the deep layer; the thermocline shoals significantly; the subsurface high salinity water shows a large decrease; and the upper mixed layer becomes thinner, and vice versa. RÉSUMÉ [Traduit par la rédaction] En nous basant sur les données mensuelles moyennes des flotteurs profileurs Argo pour la période de 2004 à 2008 et sur les données mensuelles moyennes de hauteur de la surface de la mer et de vitesses vectorielles du courant fournies par les réanalyses SODA (Simple Ocean Data Assimilation) pour la période de 1958 à 2007, nous analysons la structure tridimensionnelle du remous de Mindanao, sa variabilité saisonnière et interannuelle et son impact sur la structure thermohaline. De plus, nous discutons du déplacement du centre du remous de Mindanao et de sa relation avec les circulations océaniques. Les résultats ont montré que le remous s'étend verticalement vers le haut à partir d'une profondeur de 600 db jusqu’à une profondeur d'environ 40 db. En plus de sa forte variabilité saisonnière, la force du remous de Mindanao affiche une forte variabilité interannuelle résultant de la variabilité interannuelle dans le courant nord-équatorial (NEC), le contre-courant nord-équatorial (NECC) et le courant de Mindanao (MC). Le mouvement méridien du centre du centre du remous de Mindanao affiche une forte variabilité saisonnière et interannuelle et le mouvement zonal possède une forte variabilité saisonnière. Le mouvement méridien est lié au déplacement méridien de l'interface entre le NECC et le NEC alors que le mouvement zonal est lié au déplacement zonal de l'interface entre le MC et le bras allant vers le nord du NECC. La variabilité du remous de Mindanao peut grandement modifier la configuration de la structure thermohaline dans les couches supérieures locales de l'océan. Quand le remous est fort, l'eau froide et de faible salinité qu'il renferme se déplace vigoureusement vers le haut à partir de la couche profonde; la thermocline s'élève de façon marquée; les eaux de subsurface de forte salinité affichent une diminution importante; et la couche de mélange supérieure devient plus mince, et inversement.

Interannual variability in the Mindanao Eddy and its impact on thermohaline structure pattern

The major feature, interannual variability and variation cause of the Mindanao Eddy and its impact on the thermohaline structure are analyzed based on the Argo profiling float data, the history observed data and the SODA data. The analysis results show that the Mindanao Eddy is a permanent cyclonic meso-scale eddy and spreads vertically from about 500 m depth upward do about 50 m depth. In addition to its strong seasonal variability, the Mindanao Eddy displays a remarkable interannual variability associated with ENSO. It strengthens and expands eastward during El Nino while it weakens and retreats westward during La Nina. The interannual variability in the Mindanao Eddy may be caused by the North Equatorial Counter Current, the North Equatorial Current, the Mindanao Current and the Indonesian Through Flow. The eddy variability can have a great influence on the thermohaline structure pattern in the local upper ocean. When the eddy is strong, the cold and low salinity water inside the eddy moves violently upward from deep layer, the thermocline depth greatly shoals, and the subsurface high salinity water largely decreases, with the upper mixed layer becoming thinner, and vice versa.

Assessing the Application of Argo Profiling Float Data to the Study of the Seasonal Variation of the Hydrological Parameters and the Current Field East of Luzon Strait

The seasonal characteristics of water masses, mixed-layer depth and the current field east of Luzon Strait are studied using Argo profiling float data. Based on data from March 2006 to November 2010, the temperature-salinity relation indicates that the seasonal variation of water masses is not obvious, except that the surface temperature is lower and the salinity is higher in spring and winter; the water masses in other layers change little. The seasonal variation of the mixed-layer depth, which is deepest at over 170 m in winter and shallowest at about 25 m in summer, is also discussed. Based on the P-vector method, multi-year seasonal mean Argo data and Levitus data are used to calculate the respective current fields. The surface geostrophic current derived from altimetric data is compared with those computed from Argo data and Levitus data. It is shown that, the current field computed from Argo data, which shows the Kuroshio and eddies clearly, is similar to that obtained from altimetric data, except that the current speed is less in the former case than in the latter one; this may be related to the scarcity and uneven distribution of Argo floats, the subsequent interpolation and extrapolation errors, the shortcomings of the P-vector method, the lack of a barotropic component in the calculation or the altimetry-derived current error associated with the marine geoid, but the resultant current field is much better than that obtained from Levitus data. Moreover, Argo data have an advantage in that they can be used to derive a three-dimensional current field, whereas the altimetric data can only be used to derive the surface current field. The seasonal variations in the vertical current structure and the Kuroshio transport east of Taiwan Island are also discussed; it is found that the thickness of the northward Kuroshio is about 700 m, and the seasonal zonal variation in the main axis of the Kuroshio is obvious. RÉSUMÉ [Traduit par la rédaction] Nous étudions les caractéristiques saisonnières des masses d'eau, la profondeur de la couche de mélange et le champ de courant à l'est du détroit de Luçon à l'aide des données des flotteurs profileurs Argo. D'après les données recueillies entre mars 2006 et novembre 2010, la relation température-salinité indique que la variation saisonnière des masses d'eau n'est pas évidente, sauf que la température de surface est plus basse et la salinité plus élevée au printemps et en hiver; les masses d'eau dans les autres couches changent peu. Nous discutons aussi de la variation saisonnière de la profondeur de la couche de mélange, qui est maximale à plus de 170 m en hiver et minimale à environ 25 m en été. En nous basant sur la méthode des vecteurs P, nous utilisons les données Argo et les données Levitus pluriannuelles de moyennes saisonnières pour calculer les champs de courant respectifs. Nous comparons le courant géostrophique de surface déduit des données altimétriques avec ceux calculés à l'aide des données Argo et des données Levitus. Il apparait que le champ de courant calculé d'après les données Argo, qui montre clairement le Kuroshio et les remous, est semblable à celui obtenu des données altimétriques, sauf que la vitesse du courant est moindre dans le premier cas que dans le dernier; cela peut être lié à la rareté et à la distribution inégale des flotteurs Argo, aux erreurs subséquentes d'interpolation et d'extrapolation, aux faiblesses de la méthode des vecteurs P, au manque d'une composante barotropique dans les calculs ou à l'erreur dans le courant déduit des données altimétriques associée au géoïde marin, mais le champ de courant résultant est bien meilleur que celui obtenu à l'aide des données Levitus. De plus, les données Argo présentent l'avantage de pouvoir être utilisées pour déduire un champ de courant tridimensionnel, alors que les données altimétriques ne permettent que de déduire le champ de courant de surface. Nous discutons aussi des variations saisonnières dans la structure verticale du courant et dans le transport par le Kuroshio à l'est de l’île de Taïwan; nous trouvons que la profondeur du Kuroshio circulant vers le nord est d'environ 700 m et la variation saisonnière zonale dans l'axe principal du Kuroshio est évidente.

Research on High-Quality Soft Shadow of Building Based Shadow Map

Image rendering of shadow faces a problem existed for a long time,that is the contradiction of quality and performance. Variant algorithms are presented to ameliorate this problem,shadow map is the one which is representative for that. Even though shadow maps have been widely used for the shadow of Three-dimensional scene,some imperfection still exist in this method like aliasing problem.So,the focus of the paper is introduce an algorithm which layering the data sets of the large scale building's shadow rapidly and intelligently based shadow map. First, we ascertain the fragment which create the shadow by shadow mapping's two scan. Second, we process the float data in the depth buffer by using uniformization and render the two depth data in the texture.Then use Gauss Filter to blur.Finally,use the algorithm of BIRCH cluster the uniformization data to improve the obscure and tweened effect.This method brings reduction of aliasing problem with low overhead as well as performance to a certain extent .

Temperature versus salinity gradients below the ocean mixed layer

We characterize the global ocean seasonal variability of the temperature versus salinity gradients in the transition layer just below the mixed layer using observations of conductivity temperature and depth and profiling float data from the National Ocean Data Center's World Ocean Data set. The balance of these gradients determines the temperature versus salinity control at the mixed layer depth (MLD). We define the MLD as the shallowest of the isothermal, isohaline, and isopycnal layer depths (ITLD, IHLD, and IPLD), each with a shared dependence on a 0.2°C temperature offset. Data are gridded monthly using a variational technique that minimizes the squared analysis slope and data misfit. Surface layers of vertically uniform temperature, salinity, and density have substantially different characteristics. By examining differences between IPLD, ITLD, and IHLD, we determine the annual evolution of temperature or salinity or both temperature and salinity vertical gradients responsible for the observed MLD. We find ITLD determines MLD for 63% and IHLD for 14% of the global ocean. The remaining 23% of the ocean has both ITLD and IHLD nearly identical. It is found that temperature tends to control MLD where surface heat fluxes are large and precipitation is small. Conversely, salinity controls MLD where precipitation is large and surface heat fluxes are small. In the tropical ocean, salinity controls MLD where surface heat fluxes can be moderate but precipitation is very large and dominant.

Mesoscale variability of water masses in the Arabian Sea as revealed by ARGO floats

Abstract. By analysing ARGO float data over the last four years, a few aspects of the mesoscale variability of water masses in the Arabian Sea are described. The Red Sea Outflow Water (RSOW) is concentrated in the Southwestern Gulf of Aden, in particular when a cyclonic gyre predominates in this region. Salinities of 36.5 and temperatures of 16 °C are found in this area at depths between 600 and 1000 m. RSOW is more dilute in the eastern part of the Gulf, where intense and relatively barotropic gyres mix it with Indian ocean Central Water. RSOW is also detected along the northeastern coast of Socotra, and fragments of RSOW are found between one and three degrees of latitude north of this island. In the whole Gulf of Aden, the correlation between the deep motions of the floats and the sea-level anomaly measured by altimetry is strong, at regional scale. The finer scale details of the float trajectories are not sampled by altimetry and are often related to the anomalous water masses that the floats encounter. The Persian Gulf Water (PGW) is found in the float profiles near Ras ash Sharbatat (near 57° E, 18° N), again with 36.5 in salinity and about 18–19 °C in temperature. These observations were achieved in winter when the southwestward monsoon currents can advect PGW along the South Arabian coast. Fragments of PGW were also observed in the Arabian Sea between 18 and 20° N and 63 and 65° E in summer, showing that this water mass can escape the Gulf of Oman southeastward, during that season. Kinetic energy distributions of floats with respect to distance or angle share common features between the two regions (Gulf of Aden and Arabian Sea), in particular peaks at 30, 50 and 150 km scales and along the axis of monsoon currents. Hydrological measurements by floats are also influenced by the seasonal variations of PGW and RSOW in these regions.

Intermediate Zonal Jets in the Tropical Pacific Ocean Observed by Argo Floats*

Abstract Argo float data in the tropical Pacific Ocean during January 2003–August 2011 are analyzed to obtain Lagrangian subsurface velocities at their parking depths. Maps of mean zonal velocities at 1000 and 1500 m are presented. At both depths, a series of alternating westward and eastward zonal jets with a meridional scale of 1.5° is seen at the basin scale from 10°S to 10°N. These alternating jets, with mean speeds about 5 cm s−1, are clearly present in the western and central parts of the basin but weaken and disappear approaching the eastern coast. They are stronger in the Southern Hemisphere. Along the equator at both 1000 and 1500 m, a westward jet is seen. The jets closer to the equator are remarkably zonally coherent across the basin, but the jets farther poleward appear broken in several segments. In the western half of the basin, the 1000-m zonal jets appear to slant slightly poleward from east to west. At the western boundary in the south (east of Solomon Islands and Papua New Guinea), the alternating jets appear to connect in narrow boundary currents. Seasonal zonal velocity anomalies at 1000 and 1500 m are observed to propagate westward across the basin; they are consistent with annual vertically propagating Rossby waves superimposed on the mean zonal jets. Their meridional structure suggests that more than one meridional mode is present.

Decadal seesaw of the Central and Subtropical Mode Water formation associated with the Kuroshio Extension variability

Available Argo profiling float data from 2002 to 2011 were analyzed to examine the effect of the Kuroshio Extension (KE) current system variability on the formation of the Central Mode Water. Just north of the upstream portion of the KE at 140–152°E, formation of a lighter variety of the Central Mode Water in winter was active during the unstable period of the upstream KE in 2006–2009 and was reduced when the upstream KE was in the stable period of 2002–2005 and 2010–2011. This decadal formation variability is out of phase with that of the Subtropical Mode Water just south of the KE.

Convective mixing in the central Irminger Sea: 2002–2010

A near-continuous time series of 8 years of daily hydrographic profiles, recorded between fall 2002 and summer 2010 by moorings located in the central Irminger Sea, is presented. This record shows that convective mixing down to 400m depth occurs in most winters. Under favorable conditions, convective mixing is seen to reach much deeper. During the cold winter of 2007–2008 mixed layers reached depths of 1km. In the subsequent, more moderate winter of 2008–2009, a stronger preconditioning of the Irminger Gyre led to mixed layers down to 800m depth. The convectively formed waters in the Irminger Sea are more saline and warmer than those formed in the Labrador Sea, but potential vorticity is reduced to 0.7 10−12m−1s−1 in March 2009. Following the local wintertime convection of 2007–2008, columns of relatively fresh water were seen to arrive in the Irminger Sea in spring 2008. A comparison with float data suggests that this water mass was likely formed south–southwest of Cape Farewell. The relatively fresh water replaced the locally formed convective water mass and continued to dominate the upper 1000m of the water column until the following winter. In the winter of 2008–2009 the Irminger convective mixing strongly increased the salinity in the upper 800m, but left the intermediate salinity minimum intact. Although the water mass formed by convective mixing in the Irminger Sea differs from that formed in the Labrador Sea, the heat lost per unit area by convection is of the same order of magnitude in both basins.

Typical Surface Seasonal Circulation in the Indian Ocean Derived from Argos Floats

AbstractThis study investigates the surface circulation in the Indian Ocean using Argos float data over the period 1979–2011. The Argos observations manifest some new phenomena. The climatological annual mean circulation shows that the surface current becomes much stronger after turning around in shore in the western Indian Ocean. In the tropical Indian Ocean, the Great Whirl (GW) to the east of Somalia develops quickly in spring (April-May) as the monsoon reverses to move northward, becoming strongest in summer (June–September) and disappearing in autumn (October-November). The west end of the Agulhas retroflection can reach 18°E, and it exhibits a seasonal variation. At approximately 90°E, the Agulhas Return Current combines with the eastward South Atlantic Current and finally joins the Antarctic Circumpolar Current.

Locally enhanced wintertime air-sea interaction and deep oceanic mixed layer formation associated with the subarctic front in the North Pacific

[1] Satellite-derived high-resolution air-sea flux data and Argo float data were analyzed to reveal the fine-scale spatial structures of air-sea turbulent heat and momentum fluxes and their relationship with the deep oceanic mixed layer around the subarctic front (SAF) in the North Pacific. An important feature inferred from the satellite-derived dataset is the presence of a pair of positive and negative air-sea flux anomaly bands with a width of 100–200 km on both sides of the SAF. Such a fine-scale structure in air-sea fluxes has not been captured in previous datasets. The SAF plays a significant role in determining the fine-scale structure of air-sea fluxes. The oceanic mixed layer is deeper to the south of the SAF, and the maximum mixed layer depth is observed near the positive anomaly band in air-sea fluxes. This study concludes that active air-sea interactions due to the presence of the SAF enhances upward air-sea heat and momentum fluxes to the south of SAF and selectively produces a deep oceanic mixed layer where the formation of Transition Region Mode Water occurs.

Investigating the connection between complexity of isolated trajectories and Lagrangian coherent structures

Abstract. It is argued that the complexity of fluid particle trajectories provides the basis for a new method, referred to as the Complexity Method (CM), for estimation of Lagrangian coherent structures in aperiodic flows that are measured over finite time intervals. The basic principles of the CM are explained and the CM is tested in a variety of examples, both idealized and realistic, and in different reference frames. Two measures of complexity are explored in detail: the correlation dimension of trajectory, and a new measure – the ergodicity defect. Both measures yield structures that strongly resemble Lagrangian coherent structures in all of the examples considered. Since the CM uses properties of individual trajectories, and not separation rates between closely spaced trajectories, it may have advantages for the analysis of ocean float and drifter data sets in which trajectories are typically widely and non-uniformly spaced.

Decay of eddies at the South-West Indian Ridge

The South-West Indian Ridge in the Indian sector of the Southern Ocean is a region recognised for the creation of particularly intense eddy disturbances in the mean flow of the Antarctic Circumpolar Current. Eddies formed at this ridge have been extensively studied over the past decade using hydrographic, satellite, drifter and float data and it is hypothesised that they could provide a vehicle for localised meridional heat and salt exchange. The effectiveness of this process is dependent on the rate of decay of the eddies. However, in order to investigate eddy decay, logistically difficult hydrographic monitoring is required. This study presents the decay of cold eddies at the South-West Indian Ridge, using outputs from a high-resolution ocean model. The model’s representation of the dynamic nature of this region is fully characteristic of observations. On average, 3–4 intense and well-defined cold eddies are generated per year; these eddies have mean longevities of 5.0±2.2 months with average advection speeds of 5±2 km/day. Most simulated eddies reach their peak intensity within 1.5–2.5 months after genesis and have depths of 2000 m – 3000 m. Thereafter they dissipate within approximately 3 months. The decay of eddies is generally characterised by a decrease in their sea surface height signature, a weakening in their rotation rates and a modification in their temperature–salinity characteristics. Subantarctic top predators are suspected to forage preferentially along the edges of eddies. The process of eddy dissipation may thus influence their feeding behaviour.

Detecting coherent structures using braids

The detection of coherent structures is an important problem in fluid dynamics, particularly in geophysical applications. For instance, knowledge of how regions of fluid are isolated from each other allows prediction of the ultimate fate of oil spills. Existing methods detect Lagrangian coherent structures, which are barriers to transport, by examining the stretching field as given by finite-time Lyapunov exponents. These methods are very effective when the velocity field is well-determined, but in many applications only a small number of flow trajectories are known, for example when dealing with oceanic float data. We introduce a topological method for detecting invariant regions based on a small set of trajectories. In this method, we regard the two-dimensional trajectory data as a braid in three dimensions, with time being the third coordinate. Invariant regions then correspond to trajectories that travel together and do not entangle other trajectories. We detect these regions by examining the growth of hypothetical loops surrounding sets of trajectories, and searching for loops that show negligible growth.

The Transition Region Mode Water of the North Pacific and Its Rapid Modification

Abstract Using Argo float data, this study examined the formation region, spatial distribution, and modification of transition region mode water (TRMW), which is a recently identified pycnostad in the subtropical–subarctic transition region of the North Pacific, the basin-scale boundary region between subtropical and subarctic water masses. Analyses of the formation fields of water masses within and around the transition region reveal that TRMW forms in a wide area from the western to central transition region and is separated from the denser variety of central mode water (D-CMW) to the south by a temperature and salinity front. TRMW has temperatures of 4°–9°C and salinities of 33.3–34.0, making it colder and fresher than D-CMW. TRMW has a density range of 26.3–26.6 σθ, and thick TRMW is widely distributed in the transition region. However, the range of the T–S properties at TRMW cores is substantially reduced downstream within 10°–20° longitude from the formation region by gradually losing its fresh and cold side. It is also demonstrated that a major part of TRMW of 26.4–26.6 σθ is entrained into the mixed layer in the following winter. Quasi-Lagrangian observation by an isopycnal-following Argo float demonstrates that the double-diffusive salt-finger convection plausibly causes not only rapid erosion of the TRMW pycnostads but also an increase of salinity and temperature at the TRMW cores, at least to some degree. It is demonstrated that strong salt fingering within TRMW is probably caused by geostrophic currents with vertical shear crossing the density-compensating T–S front that brings warm and saline water to the upper TRMW and creates instability in the salinity stratification. This modification process could explain why water that is subducted from the transition region and constitutes the pycnocline of the subtropical gyre in the North Pacific has different T–S properties from the winter mixed layer of the transition region. This knowledge about the modification process of subducted water in the transition region would help to model the permanent pycnocline structure more realistically and to clarify how large signals of decadal and multidecadal variability of sea surface temperature in this region are propagated into the ocean interior.

Real-time estimation of pH and aragonite saturation state from Argo profiling floats: Prospects for an autonomous carbon observing strategy

[1] We demonstrate the ability to obtain accurate estimates of pH and carbonate mineral saturation state (Ω) from an Argo profiling float in the NE subarctic Pacific. Using hydrographic surveys of the NE Pacific region, we develop empirical algorithms to predict pH and Ω using observations of temperature (T) and dissolved O2. We attain R2 values greater than 0.98 and RMS errors of 0.018 (pH), 0.052 (Ωarag), and 0.087 (Ωcalc) for data between 30–500 m, σθ < 27.1. After calibrating optode-based O2 data, we apply the algorithms to T and O2 data from an Argo profiling float to produce a 14 month time-series of estimated pH and Ωarag in the upper water column of the NE subarctic Pacific. Comparison to independent data collected nearby in 2010 indicates pH and Ωarag estimates are robust. Although the method will not allow detection of anthropogenic trends in pH or Ωarag, this approach will provide insight into natural variability and the key biogeochemical controls on these parameters. Most importantly, this work demonstrates that an assemblage of well-calibrated regional algorithms and Argo float data can be used as a low-cost, readily-deployable component of a global ocean carbon observing strategy.