scholarly journals Uppermost Mantle Velocity beneath the Mid-Atlantic Ridge and Transform Faults in the Equatorial Atlantic Ocean

2020 ◽  
Author(s):  
Guilherme W. S. de Melo ◽  
Ross Parnell-Turner ◽  
Robert P. Dziak ◽  
Deborah K. Smith ◽  
Marcia Maia ◽  
...  
Keyword(s):  
Atlantic Ocean ◽  
Upper Mantle ◽  
Equatorial Atlantic ◽  
Uppermost Mantle ◽  
Transform Faults ◽  
Equatorial Atlantic Ocean ◽  
Mid Atlantic Ridge ◽  
Mantle Velocity ◽  
Ray Paths

ABSTRACT Seismic rays traveling just below the Moho provide insights into the thermal and compositional properties of the upper mantle and can be detected as Pn phases from regional earthquakes. Such phases are routinely identified in the continents, but in the oceans, detection of Pn phases is limited by a lack of long-term instrument deployments. We present estimates of upper-mantle velocity in the equatorial Atlantic Ocean from Pn arrivals beneath, and flanking, the Mid-Atlantic Ridge and across several transform faults. We analyzed waveforms from 50 earthquakes with magnitude Mw>3.5, recorded over 12 months in 2012–2013 by five autonomous hydrophones and a broadband seismograph located on the St. Peter and St. Paul archipelago. The resulting catalog of 152 ray paths allows us to resolve spatial variations in upper-mantle velocities, which are consistent with estimates from nearby wide-angle seismic experiments. We find relatively high velocities near the St. Paul transform system (∼8.4  km s−1), compared with lower ridge-parallel velocities (∼7.7  km s−1). Hence, this method is able to resolve ridge-transform scale velocity variations. Ray paths in the lithosphere younger than 10 Ma have mean velocities of 7.9±0.5  km s−1, which is slightly lower than those sampled in the lithosphere older than 20 Ma (8.1  km±0.3  s−1). There is no apparent systematic relationship between velocity and ray azimuth, which could be due to a thickened lithosphere or complex mantle upwelling, although uncertainties in our velocity estimates may obscure such patterns. We also do not find any correlation between Pn velocity and shear-wave speeds from the global SL2013sv model at depths <150  km. Our results demonstrate that data from long-term deployments of autonomous hydrophones can be used to obtain rare and insightful estimates of uppermost mantle velocities over hundreds of kilometers in otherwise inaccessible parts of the deep oceans.

scholarly journals A new method for continuous measurements of oceanic and atmospheric N<sub>2</sub>O, CO and CO<sub>2</sub>: performance of off-axis integrated cavity output spectroscopy (OA-ICOS) coupled to non-dispersive infrared detection (NDIR)

Ocean Science ◽  
2013 ◽  
Vol 9 (6) ◽  
pp. 1071-1087 ◽  
Author(s):  
D. L. Arévalo-Martínez ◽  
M. Beyer ◽  
M. Krumbholz ◽  
I. Piller ◽  
A. Kock ◽  
...  
Keyword(s):  
Atlantic Ocean ◽  
Response Times ◽  
Equatorial Atlantic ◽  
Atmospheric Measurements ◽  
Long Term Stability ◽  
Ascension Island ◽  
Cavity Output ◽  
Equatorial Atlantic Ocean ◽  
Equatorial Upwelling

Abstract. A new system for continuous, highly resolved oceanic and atmospheric measurements of N2O, CO and CO2 is described. The system is based upon off-axis integrated cavity output spectroscopy (OA-ICOS) and a non-dispersive infrared analyzer (NDIR), both coupled to a Weiss-type equilibrator. Performance of the combined setup was evaluated by testing its precision, accuracy, long-term stability, linearity and response time. Furthermore, the setup was tested during two oceanographic campaigns in the equatorial Atlantic Ocean in order to explore its potential for autonomous deployment onboard voluntary observing ships (VOS). Improved equilibrator response times for N2O (2.5 min) and CO (45 min) were achieved in comparison to response times from similar chamber designs used by previous studies. High stability of the OA-ICOS analyzer was demonstrated by low optimal integration times of 2 and 4 min for N2O and CO respectively, as well as detection limits of < 40 ppt and precision better than 0.3 ppb Hz–1/2. Results from a direct comparison of the method presented here and well-established discrete methods for oceanic N2O and CO2 measurements showed very good consistency. The favorable agreement between underway atmospheric N2O, CO and CO2 measurements and monthly means at Ascension Island (7.96° S 14.4° W) further suggests a reliable operation of the underway setup in the field. The potential of the system as an improved platform for measurements of trace gases was explored by using continuous N2O and CO2 data to characterize the development of the seasonal equatorial upwelling in the Atlantic Ocean during two R/V Maria S. Merian cruises. A similar record of high-resolution CO measurements was simultaneously obtained, offering, for the first time, the possibility of a comprehensive view of the distribution and emissions of these climate-relevant gases in the area studied. The relatively simple underway N2O/CO/CO2 setup is suitable for long-term deployment onboard research and commercial vessels although potential sources of drift, such as cavity temperature, and further technical improvements towards automation, still need to be addressed.

scholarly journals Occurrence of Omura’s whale, Balaenoptera omurai (Cetacea: Balaenopteridae), in the Equatorial Atlantic Ocean based on Passive Acoustic Monitoring

2020 ◽  
Author(s):  
Sergio C Moreira ◽  
Marcelo Weksler ◽  
Renata S Sousa-Lima ◽  
Marcia Maia ◽  
Alexey Sukhovich ◽  
...  
Keyword(s):  
Atlantic Ocean ◽  
Northeastern Brazil ◽  
Equatorial Atlantic ◽  
Equatorial Atlantic Ocean ◽  
Mid Atlantic Ridge ◽  
Vocal Activity ◽  
Passive Acoustic ◽  
Warm Temperate ◽  
The Western Pacific ◽  
Indian And Atlantic Oceans

Abstract The current known distribution of Omura’s whale includes the tropical and warm temperate waters of the western Pacific, Indian, and Atlantic Oceans. Evidence of their presence in the Atlantic Ocean is based on beach cast specimens found on the coasts of Mauritania (North Atlantic) and Northeastern Brazil (South Atlantic). The present study characterizes the occurrence of this species in the São Pedro and São Paulo Archipelago (SPSPA), on the mid-Atlantic ridge between South America and Africa, based on autonomous recording systems. Acoustic signals were similar, but not identical, to B. omurai vocalizations recorded off the coast of Madagascar. Although these signals were recorded for only 11 months, there are peaks in vocal activity between May and June in the vicinities of SPSPA, suggesting either a shift in distribution within the Atlantic equatorial waters or seasonality in the species’ vocal behavior in this region. The first acoustic records of Omura’s whales in the Equatorial Atlantic suggest that these animals may also use deep-water habitats, in addition to the shallow-water habitat use observed in other regions.

scholarly journals Geophysical and geochemical evidence for cold upper mantle beneath the Equatorial Atlantic Ocean

2008 ◽  
Vol 26 (1) ◽  
pp. 69-86 ◽  
Author(s):  
Susanna Eleonora Sichel ◽  
Sonia Esperança ◽  
Akihisa Motoki ◽  
Marcia Maia ◽  
Mary F. Horan ◽  
...  
Keyword(s):  
Atlantic Ocean ◽  
Upper Mantle ◽  
Equatorial Atlantic ◽  
Geochemical Evidence ◽  
Equatorial Atlantic Ocean

Geothermal asymmetry in transform faults of the equatorial Atlantic Ocean

2017 ◽  
Vol 475 (1) ◽  
pp. 836-839 ◽  
Author(s):  
M. D. Khutorskoi ◽  
E. A. Teveleva ◽  
L. V. Podgornykh
Keyword(s):  
Atlantic Ocean ◽  
Equatorial Atlantic ◽  
Transform Faults ◽  
Equatorial Atlantic Ocean

scholarly journals A new method for continuous measurements of oceanic and atmospheric N<sub>2</sub>O, CO and CO<sub>2</sub>: performance of off-axis integrated cavity output spectroscopy (OA-ICOS) coupled to non-dispersive infrared detection (NDIR)

2013 ◽  
Vol 10 (4) ◽  
pp. 1281-1327 ◽  
Author(s):  
D. L. Arévalo-Martínez ◽  
M. Beyer ◽  
M. Krumbholz ◽  
I. Piller ◽  
A. Kock ◽  
...  
Keyword(s):  
Atlantic Ocean ◽  
Response Times ◽  
Equatorial Atlantic ◽  
Atmospheric Measurements ◽  
Long Term Stability ◽  
Ascension Island ◽  
Cavity Output ◽  
Equatorial Atlantic Ocean ◽  
Equatorial Upwelling

Abstract. A new system for continuous, highly-resolved oceanic and atmospheric measurements of N2O, CO and CO2 is described. The system is based upon off-axis integrated cavity output spectroscopy (OA-ICOS) and a non-dispersive infrared analyzer (NDIR) both coupled to a Weiss-type equilibrator. Performance of the combined setup was evaluated by testing its precision, accuracy, long-term stability, linearity and response time. Furthermore, the setup was tested during two oceanographic campaigns in the equatorial Atlantic Ocean in order to explore its potential for autonomous deployment onboard voluntary observing ships (VOS). Improved equilibrator response times for N2O (2.5 min) and CO (45 min) were achieved in comparison to response times from similar chamber designs used by previous studies. High stability of the OA-ICOS analyzer was demonstrated by low optimal integration times of 2 and 4 min for N2O and CO respectively, as well as detection limits of < 40 ppt and precision better than 0.3 ppb Hz−1/2. Results from a direct comparison of the method presented here and well-established discrete methods for oceanic N2O and CO2 measurements showed very good consistency. The favorable agreement between underway atmospheric N2O, CO and CO2 measurements and monthly means at Ascension Island (7.96° S 14.4° W) further suggests a reliable operation of the underway setup in the field. The potential of the system as an improved platform for measurements of trace gases was explored by using continuous N2O and CO2 data to characterize the development of the seasonal equatorial upwelling in the Atlantic Ocean during two R/V Maria S. Merian cruises. A similar record of high-resolution CO measurements was simultaneously obtained offering for the first time the possibility of a comprehensive view on the distribution and emissions of these climate relevant gases on the area. The relatively simple underway N2O/CO/CO2 setup is suitable for long-term deployment on board of research and commercial vessels although potential sources of drift such as cavity temperature and further technical improvements towards automation still need to be addressed.

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