P. Vélez-Belchí

Transport variability in the Lanzarote passage (eastern boundary current of the North Atlantic subtropical Gyre)

Observations from a four-year current meter mooring at 28°44′N, 13°28′W in the Lanzarote passage are used to describe the transport variability of the Eastern Boundary Current of the North Atlantic Subtropical Gyre. Three different water masses are found in the passage: North Atlantic Central Water in the upper levels (roughly Full-size image (<1 K)), Antarctic Intermediate Water (roughly Full-size image (<1 K)) and Mediterranean Water in the layer above the bottom at Full-size image (<1 K). The mean southward transport of NACW is Full-size image (<1 K)Full-size image (<1 K) which is the transport of the easternmost branch of the Canary Current. Fluctuations of NACW transport are large, ranging from Full-size image (<1 K) southward to Full-size image (<1 K) northward. Every autumn a consistent northward transport is observed, which may be related with the eastern boundary upwelling dynamics. The mean transports of AAIW and MW are Full-size image (<1 K) northward and Full-size image (<1 K) southward, respectively. Fluctuations of transport of AAIW and MW are large, from 1.0 to Full-size image (<1 K) and from −0.32 to Full-size image (<1 K), respectively. Thus, the mass transports for each water mass show a high standard deviation of comparable magnitude to the mean. This highlights the importance of the temporal variability of the currents in this passage. A remarkable feature of our observations is that the mean transports of NACW and AAIW during an El Nino event are significantly different.

The submarine volcano eruption at the island of El Hierro: physical-chemical perturbation and biological response

On October 10 2011 an underwater eruption gave rise to a novel shallow submarine volcano south of the island of El Hierro, Canary Islands, Spain. During the eruption large quantities of mantle-derived gases, solutes and heat were released into the surrounding waters. In order to monitor the impact of the eruption on the marine ecosystem, periodic multidisciplinary cruises were carried out. Here, we present an initial report of the extreme physical-chemical perturbations caused by this event, comprising thermal changes, water acidification, deoxygenation and metal-enrichment, which resulted in significant alterations to the activity and composition of local plankton communities. Our findings highlight the potential role of this eruptive process as a natural ecosystem-scale experiment for the study of extreme effects of global change stressors on marine environments.

The Canary Basin contribution to the seasonal cycle of the Atlantic Meridional Overturning Circulation at 26°N

This study examines the seasonal cycle of the Atlantic Meridional Overturning Circulation (AMOC) and its eastern boundary contributions. The cycle has a magnitude of 6 Sv, as measured by the RAPID/MOCHA/WBTS project array at 26°N, which is driven largely by the eastern boundary. The eastern boundary variations are explored in the context of the regional circulation around the Canary Islands. There is a 3 month lag between maximum wind forcing and the largest eastern boundary transports, which is explained in terms of a model for Rossby wave generated at the eastern boundary. Two dynamic processes take place through the Lanzarote Passage (LP) in fall: the recirculation of the Canary Current and the northward flow of the Intermediate Poleward Undercurrent. In contrast, during the remaining seasons the transport through the LP is southward due to the Canary Upwelling Current. These processes are linked to the seasonal cycle of the AMOC.

IEOOS: the Spanish Institute of Oceanography Observing System

Since its foundation, 100 years ago, the Spanish Institute of Oceanography (IEO) has been observing and measuring the ocean characteristics. Here is a summary of the initiatives of the IEO in the field of the operational oceanography. Some systems like the tide gauges network has been working for more than 70 years. The standard sections began at different moments depending on the local projects, and nowadays there are more than 180 coastal stations and deep-sea ones that are systematically sampled, obtaining physical and biochemical measurements. At this moment, the Observing System includes six permanent moorings equipped with current meters, an opensea ocean-meteorological buoy offshore Santander and a sea-surface temperature satellite image station. It also supports the Spanish contribution to the Argo international programme with 47 deployed profilers, and continuous monitoring thermosalinometers, meteorological stations and vesselmounted acoustic Doppler current profilers on the research vessel fleet. The system is completed with the contribution to the Northwest Iberian peninsula and Gibraltar observatories, and the development of regional prediction models. All these systematic measurements allow the IEO to give responses to ocean research activities, official agencies requirements and industrial and main society demands such as navigation, resource management, risks management, recreation, as well as for management development pollution-related economic activities or marine ecosystems. All these networks are linked to international initiatives, framed largely in supranational programmes of Earth observation sponsored by the United Nations or the European Union. The synchronic observation system permits a spatio-temporal description of some events, such as new deep water formation in the Mediterranean Sea and the injection of heat to intermediate waters in the Bay of Biscay after some colder northern storms in winter 2005.

Wind-driven cross-equatorial flow in the Indian Ocean

AbstractMeridional velocity, mass, and heat transport in the equatorial oceans are difficult to estimate because of the nonapplicability of the geostrophic balance. For this purpose a steady-state model is utilized in the equatorial Indian Ocean using NCEP wind stress and temperature and salinity data from the World Ocean Atlas 2005 (WOA05) and Argo. The results show a Somali Current flowing to the south during the winter monsoon carrying −11.5 ± 1.3 Sv (1 Sv ≡ 106 m3 s−1) and −12.3 ± 0.3 Sv from WOA05 and Argo, respectively. In the summer monsoon the Somali Current reverses to the north transporting 16.8 ± 1.2 Sv and 19.8 ± 0.6 Sv in the WOA05 and Argo results. Transitional periods are considered together and in consequence, there is not a clear Somali Current present in this period. Model results fit with in situ measurements made around the region, although Argo data results are quite more realistic than WOA05 data results.

Changes in Temperature and Salinity Tendencies of the Upper Subtropical North Atlantic Ocean at 24.5°N

Abstract Strong interest in multidecadal changes in ocean temperature and heat transport has resulted in the occupation of the North Atlantic Ocean hydrographic transect along 24.5°N five times since 1957, more than any other transoceanic section in the world. This latitude is chosen because it is where the northward ocean transport of heat in the Atlantic reaches its maximum. An analysis of the five oceanographic cruises at this latitude shows that there has been a significant cooling of −0.15°C in the upper ocean (600–1800-dbar range) over the last 7 years, from 1998 to 2004, which is in contrast to the warming of 0.27°C observed from 1957 to 1998. Salinity shows a similar change in tendency, with freshening since 1998. For the upper ocean at 24.5°N, 1998 was the warmest and saltiest year since 1957. Data from the Argo network are used to corroborate the strong cooling and freshening since 1998, showing a −0.13°C cooling in the period between 1998 and 2006 and revealing interannual variability between 2...

The Impact of New Multi-platform Observing Systems in Science, Technology Development and Response to Society Needs; from Small to Large Scales…

New monitoring technologies are key components of ocean observatories, also called marine research infrastructures being implemented in the worlds oceans. As a result, new capabilities to characterise, in quasi-real time, the ocean state and its variability at small scales exist today. The challenge is the integration of theses multiplatform observing and forecasting systems to (a) monitor the variability at small scales (e.g. mesoscale/weeks) in order to (b) resolve the sub-basin/seasonal and inter-annual variability and by this (c) establish the decadal variability, understand the associated biases and correct them. The challenge is also to change focus and now monitor from small to large scales. SOCIB is leading this new small to large-scale multi-platform approach in ocean observation. Some examples are presented and discussed together with initial ideas on the optimal design of an observational network in the world oceans, responding to science priorities, technology development and response to strategic society needs.

On the seasonal variability of the Canary Current and the Atlantic Meridional Overturning Circulation

The Atlantic meridional overturning circulation (AMOC) is continually monitored along 26°N by the RAPID-MOCHA array. Measurements from this array show a 6.7 Sv seasonal cycle for the AMOC, with a 5.9 Sv contribution from the upper-mid-ocean. Recent studies argue that the dynamics of the eastern Atlantic is the main driver for this seasonal cycle; specifically, Rossby waves excited south of the Canary Islands. Using inverse modelling, hydrographic, mooring and altimetry data, we describe the seasonal cycle of the ocean mass transport around the Canary Islands and at the eastern boundary, under the influence of the African slope, where eastern component of the RAPID-MOCHA array is situated. We find a seasonal cycle of -4.1±0.5 Sv for the oceanic region of the Canary Current, and +3.7±0.4 Sv at the eastern boundary. This seasonal cycle along the eastern boundary is in agreement with the seasonal cycle of the AMOC, that requires the lowest contribution to the transport in the upper-mid-ocean to occur in fall. However, we demonstrate that the linear Rossby wave model used previously to explain the seasonal cycle of the AMOC is not robust, since it is extremely sensitive to the choice of the zonal range of the wind stress curl and produces the same results with a Rossby wave speed of zero. We demonstrate that the seasonal cycle of the eastern boundary is due to the recirculation of the Canary Current and to the seasonal cycle of the poleward flow that characterizes the eastern boundaries of the oceans.

Eddy-Induced Variability in a Transatlantic Section: Argo Observing System-Gyroscope 0302 Cruise Comparison

Ocean hydrological sections provide a very useful mean to study the ocean circulation as well as to determine water mass properties and to estimate fluxes. One basic method for their analysis is the spatial interpolation of data, obtained from a set of predefined stations, into a regular grid for contouring isolines and for further calculations. The shortest length scales that can be solved are limited by the distance between stations. Some of these scales, though resoluble by the sampling design, may be, with respect to time variability, shorter than the time that is needed to complete the section. This situation can produce a lack of synopticity in the obtained data, which is not usually addressed in oceanographic studies because the sequential repetition of oceanographic surveys is not an easy task. Here two samplings are compared—one by CTD- and another by Array for Real-Time Geostrophic Oceanography (Argo)-type profilers—of the same zonal section with a 5-day delay. The integral time scale for the mesoscale field is around 11 days, which implies that the mesoscale signal obtained from consecutive transmissions of the profilers are weakly correlated. The mesoscale field in a transatlantic section, which typically takes 20 days to be carried out, cannot be considered as synoptic.

A comparison with the Argo observing system—Gyroscope 0302 cruise

Abstract In March 2002, 20 Argo profilers were deployed in the Subtropical North Atlantic, within the European project Gyroscope. In this contribution we compare the θ-distribution on a hydrographical section along the 24.5°N parallel using two different data sets. The first set consists of the first data transmitted by an array of autonomous profilers deployed along the section, and the second set is made up of CTD stations accomplished during the deployment and discusses the representativeness of the field at different scales.