Fig 9 - uploaded by Xue-Gang Chen
Content may be subject to copyright.
Source publication
The chemical and isotopic compositions of gases discharging from shallow-water hydrothermal vents at Kueishantao (KST, northeast Taiwan) have been studied since 2000. In this paper, we present new data gathered from 2010 to 2014. The main component is CO2 (162–882 mmol/mol), followed by N2 (33–634 mmol/mol), CH4 (18–190 mmol/mol), and H2S (b.d.l.–1...
Context in source publication
Context 1
... summary, we investigated the chemical and isotopic characteristics of KST bubbling gases and studied their sources and evolution processes (Fig. 9). The primary gas species in the reaction zone were CO 2 and He, originat- ing from the mantle, whereas CH 4 (also present) may have been generated abiotically (e.g., by FTT reactions). More than 70% of the He was derived from the mantle, accord- ing to the R/R a ratios (5.9-8.1). The CO 2 exhibited d 13 C VPDB values ranging from -8.2 ...
Citations
... The low H 2 S concentration group was reported in SVs of Milos island (Greece; 4.9 mmol mol −1 ; Dando et al., 1995), Louise Harbor (Papua New Guinea; 8 mmol mol −1 ; Pichler et al., 1999a), Tutum Bay (Papua New Guinea; < 0.3 mmol mol −1 ; Pichler et al., 1999b), Punta Mita (Mexico; < 0.01 mmol mol −1 ; Prol-Ledesma et al., 2002), and Bahía Concepción (Mexico; undetected; Forrest et al., 2005). SVs off Kueishan (KS) Island in Taiwan belong to the group of high H 2 S concentrations (up to 172.4 mmol mol −1 ; Chen et al., 2016). These SVs are further distinguished according to the color of plumes, e.g., white vents (WVs) and yellow vents (YVs). ...
... In this study, a WV (24.83404 • N, 121.96172 • E) and a YV (24.83553 • N, 121.96361 • E) were sampled in July and August 2010, and the distance between the two vents was about 100 m. The vent plume temperature varied between 41-62 • C in the WV and 54-121 • C in the YV Chen et al., 2016;Hung et al., 2019;Lebrato et al., 2019). The pH in the WV was 4.83-5.74, ...
... mmol mol −1 , respectively) and N 2 (309.9±72.4 and 65.1±17.0 mmol mol −1 , respectively; Chen et al., 2016). The recorded environmental parameters of our sampling lo-cations on 4 and 24 August 2010 in the WV and YV included temperature, pH, and depth (i.e., 25.0 and 26.7 • C, 7.3 and 7.8, and 17 and 7 m, respectively; Table 1). ...
The shallow-water hydrothermal vents (SVs) located off Kueishan (KS) Island, Taiwan, are one of the world's most intensively studied vent systems. It has long been known that white vents (WVs) and yellow vents (YVs) differ in the color and composition of the vent plumes. The endemic vent crabs (Xenograpsus testudinatus) are abundant in both vent types, and ovigerous females migrate to the vent periphery with a distance of 100–200 m to release their offspring. However, most research on the vent crabs was associated with WV or unspecified vent areas. To increase our knowledge of the crabs dwelling in other vent types, we compared the feeding habits of the vent crabs living in WV and YV with 2 sampling months. Specifically, we examined the benthic community of WV and YV, the isotopic niche width, and protein expression patterns of the crabs from the two vents at a distance of 100 m and sampled in July and August 2010. The coverage of sessile organisms and low-mobility fauna in WV was more abundant than in YV, based on the survey in August 2010. The δ13C and δ15N values of crabs differed spatially and temporally (multivariate analysis of variance test; p<0.05). The niche width of the vent crabs from YV-August (0.88 ‰2) narrowed substantially compared to the rest, i.e., YV-July (2.94 ‰2), WV-July (2.88 ‰2), and WV-August (3.62 ‰2; p<0.05), respectively. Based on the protein expression patterns, the vent crabs exhibited three groups, i.e., WV-July and YV-July, WV-August, and YV-August, respectively. Our results indicated that the dwelling crabs were associated with their living vent, and within-vent variability was more noticeable in YV compared to WV. We suggested that vent crabs inhabit their resident vent. Even at a scale of meters, trans-vent movement is probably rare as an adaptation to minimize predation risk.
... More than 92% of the dry vent gas is CO 2 , and a pH less than 2 was observed in the vent fluids (C.-T. A. Chen, Zeng, et al., 2005;Yang et al., 2005). Previous studies have characterized the δ 13 C values of vent CO 2(g) (hereinafter vCO 2 ) (X. G. Chen et al., 2016), and assessed the impact of vCO 2 on the carbonate chemistry of ambient seawater (Lin et al., 2019). The δ 13 C values of dissolved inorganic carbon (DIC) in the vertical plume have also been reported (Lin et al., 2020). ...
... Although the 2014 WV gas had a δ 13 C value within the range known for KST vents (X. G. Chen et al., 2016), the possibility of isotopic fractionation could not be excluded. Hence, the δ 13 C values of both 2014 gas samples were excluded from further discussion. ...
... The δ 13 C values are consistent with previously reported data (X. G. Chen et al., 2016). ...
We report radiocarbon and stable carbon isotope measurements from vent gas (CO2(g)), dissolved inorganic carbon (DIC), and particulate organic carbon (POC), from two vents of the Kueishantao (KST) shallow-water hydrothermal system, offshore northeast Taiwan. The purpose of this research is to investigate how magmatic-sourced carbon enters various carbon pools in the hydrothermal system. We utilize a precipitation method to eliminate sulfur compounds from CO2 samples to facilitate Accelerator Mass Spectrometry (AMS) analysis, and evaluate radiocarbon background levels during processing in order to characterize hydrothermal-sourced CO2 that contains negligible radiocarbon. The result shows that both CO2(g) and DIC in the fluids below two vent orifices fall within a narrow range of fraction of modern carbon (F14C) from 0.013 to 0.136 and δ13C from -8.3‰ to -5.1‰. The F14C values correspond to approximately 90% magmatic-sourced carbon in CO2(g) and DIC. A combination of equilibrium and kinetic isotopic fractionation can adequately explain relatively high CO2(g) δ13C to DIC beneath vent orifices. Above the vent orifices, DIC becomes enriched in both 14C and 13C as a result of physical mixing with ambient seawater. POC F14C values confirm a significant magmatic carbon contribution into the POC pool within the KST system with rapid hydrothermal circulation. Our results identify the physiochemical processes responsible for magmatic carbon migration from CO2(g) into the DIC pool, and demonstrate how a dual carbon isotope approach can serve as an effective tool in understanding carbon flow in high temperature-low pH hydrothermal systems.
... The low H 2 S concentration group was reported in SVs of Louise Harbor (8 mmol mol -1 , Papua New Guinea, Pichler et al., 1999a), Milos Island (4.9 mmol mol -1 , Greece, Dando et al., 1995), Tutum Bay (< 0.3 mmol mol -1 , Papua New Guinea, Pichler 30 et al. 1999b), Punta Mita (< 0.01 mmol mol -1 , Mexico, Prol-Ledesma et al., 2002), and Bahía Concepción (undetected, Mexico, Forrest et al., 2005). In contrast, high H 2 S concentrations were only recorded in SVs off Kueishan (KS) Islet, Taiwan (as high as 172.4 mmol mol -1 , Chen et al., 2016). These SVs are further distinguished according to the color of plumes, e.g., white vent (WV) and yellow vent (YV). ...
The shallow-water hydrothermal vents (SVs) located off Kueishan (KS) Islet, Taiwan, are one of the most intensively studied vent systems. Here, two distinct vent types were identified as white vents (WVs) and yellow vents (YVs), based on the color, physical and chemical characteristics of vent plumes. The endemic vent crabs (Xenograpsus testudinatus) are abundant in both WVs and YVs. However, most research on the vent crabs was associated with WV or unspecified vent areas. Studies on crabs dwelling in other vent types are rare. Here, we investigated the feeding habit of crabs inhabiting YV and made a comparison with WV crabs. Specifically, we examined the benthic community of WV and YV, isotopic niche width, and protein expression patterns of the crabs from the two vent types at a distance of 100 m. The coverage of sessile organisms and low-mobility fauna in WV were more abundant than in YV. The δ13C and δ15N values were insignificantly different between crabs from WV and YV. The niche width of crabs from WV was significantly broader than those from YV, shown as SEAc areas of 3.62 ‰2 vs. 0.88 ‰2 (p < 0.05). The overlap percentages in WV and YV were 23.9 % and 97.9 %, respectively. The food sources of crabs in WV were more diverse than those in YV. Based on the protein expression patterns, the vent crabs were classified into WV- and YV-dwellings. Our results revealed that the feeding habits of the endemic vent crabs (X. testudinatus) are adapted to their vent types at a distance of 100 m, and the trans-vent movement is uncommon.
... The Ca, Mg and K are significantly correlated with each other, indicating the same source of seawater [45]. The gas component is mainly CO 2 , followed by N 2 , CH 4 and H 2 S [46]. ...
Strontium (Sr), hydrogen (H) and oxygen (O) in vent fluids are important for understanding the water–rock interaction and hydrothermal flux in hydrothermal systems. We have analyzed the Sr, H and O isotopic compositions of seawater, vent fluid and hydrothermal plume samples in the Kueishantao hydrothermal field, as well as their calcium (Ca), total sulfur (S), Sr, arsenic (As), stibium (Sb), chlorine (Cl) and manganese (Mn) concentrations for understanding the origin and processes of fluids. The results suggest that most As, Sb and Mn are leached from andesitic rocks into the fluids, and most Ca and Cl remained in the deep reaction zone during the fluid–andesitic rock interaction. The ranges of 87Sr/86Sr, δDV-SMOW and δ18OV-SMOW values in the yellow spring, white spring and plumes are small. The 87Sr/86Sr, δDV-SMOW and δ18OV-SMOW values of fluids and plumes are like those of ambient seawater, indicating that the Sr, H and O of vent fluids and hydrothermal plumes are derived primarily from seawater. This suggests that the interaction of andesite and subseafloor fluid is of short duration and results in the majority of As, Sb and Mn being released into fluids, while most Ca and Cl remained in the deep reaction zone. In addition, there was no significant variation of Sr, H and O isotopic compositions in the upwelling fluid, keeping the similar isotopic compositions of seawater. There are obvious correlations among the pH values, As and Sb concentrations, and H isotopic compositions of the vent fluids and hydrothermal plumes, implying that the As and Sb concentrations and H isotopic compositions can trace the dispersion of plumes in the ambient seawater. According to the Sr concentrations and 87Sr/86Sr values, the water/rock ratios are 3076~8124, which is consistent with the idea that the interaction between fluid and andesite at the subseafloor is of short duration. The hydrothermal flux of Sr discharged from the yellow spring into the seawater is between 2.06 × 104 and 2.26 × 104 mol/yr, and the white spring discharges 1.18 × 104~1.26 × 104 mol/yr Sr if just andesites appear in the reaction zone.
... The results of the isotopic analysis of the pore water show that the methane in the shallow sediments was generated via the microbially mediated processes of carbon dioxide reduction (δ 13 C CH 4 < −50‰, microbial methane) and/or thermal cracking of organic matter (δ 13 C CH 4 > −50‰, thermogenic methane) [16,28]. These results seem to agree with the summary of the origin of methane-rich natural gas in the backarc region of active magmatism in the southernmost end of the OT [42] and the Western Pacific [43]. However, its [15]). ...
... The studies of the seawater in the OT are aimed at pinpointing the sites of the enhanced concentration of dissolved methane, assessing the origin of the carbon, and figuring out the methane flux at the sedimentseafloor and the sea-air interfaces [42,49,50]. The most important contributors to the dissolved carbon in the seawater are hydrothermal vents and cold seeps, and the DIC through the latter ones constitutes up to 14.3% of the total amount in the seawater [49]. ...
It has been two decades since the cold seeps were firstly found in the Okinawa Trough (OT). The scientific cruises and the geological surveys since then have unveiled the currently active submarine methane seeps and significantly improved the understanding of methane seeps in the back-arc basin of the OT. In this paper, we review the up-to-date progress of the research of methane seepages then put forward the promising, yet challenging, outlook by listing the unsolved questions of the cold seeps in the OT. Multiple approaches and techniques, including seismic and echo-sounder recording, dredging, gravity-piston and ROV coring, seafloor drilling, and isotopic and microarray-based genomic analysis, have been used to reveal the geological processes responsible for the seeping activities and the biogeochemical processes related to them. The geophysical signature associated with gas seeps mainly includes the acoustic turbidity in the subsurface, the anomaly of the backscattering intensity at the seabed, and the gas plumes observed in the water column. Pore water and methane-derived authigenic carbonate archive the intensification of methane seepage and the paleoenvironment changes at different time scales. The methane feeding of the seeps in the OT was generated mostly via the microbially mediated process and has an origin mixed by thermogenic hydrocarbon gas in the middle OT. Sulfate-driven and Fe-driven anaerobic oxidations of methane are suggested to be the key biogeochemical processes, which would shape the material cycling in the seeping environment. The future research on the cold seeps in the OT is worth looking forward to due to its geographic and potential geologic links with the nearby hydrothermal activities. Multidisciplinary studies are expected to concentrate on their link with the undiscovered gas hydrates, the amount of methane transferring into the oceans and its impact on the climatic change, and the evolution of the seeping activities accompanied by the biogeochemical processes.
1. Introduction
Cold seeps are seafloor expressions of the upward migration of methane-rich gases through the marine sedimentary succession [1–3]. This migration involves the varying gas fluxes with time at the seabed and the alternation between the seeping and the diffusion of gases within an area smaller than a couple of square kilometers at one seeping site [1]. It has attracted increasing scientific attention since it was detected by side-scan sonar offshore Nova Scotia, Canada [4]. Methane escaping from the submarine seeps constitutes an important part of the output of the carbon from the marine sediments into the oceans [5]. This makes the worldwide seeps a window to evaluate the impact of the methane on climatic change and study the diverse methane-dependent ecosystem [6]. The predictable consequences of considerable methane seepage from seafloor include the amplification of ocean deoxygenation and acidification and, which is still under debate, the atmospheric greenhouse gas concentrations [7–9].
The cold seeps out of the shelf of the East China Sea in the Okinawa Trough (OT) were firstly found along its western slope of the middle part (~26.2°N) during the scientific cruise in 2000 [10]. Since then, there has been some scientific cruises and geological surveys over the broad marine region (Figures 1 and 2), which provide geophysical and geochemical data (Tables 1 and 2) for continuous research and significantly contribute to the understanding of the methane seepage in the OT. Multiple ship-based approaches have been used to focus on these seeps of different spatiotemporal dimensions. The acoustic ones mainly consist of seismic and echo-sounder, and together reveal the locations of the seeps and their features from the subsurface and the seabed to the water column [10–16]. The pore water and the authigenic minerals serve as the main geological record of the seeps and have been sampled by grabbing of remotely operated vehicles (ROVs), dredging and gravity-piston coring, and seafloor drilling. Geochemical investigation of these samples reveals the involved biogeochemical processes, the origin of the methane, the interaction between the pore fluids and the seep-impacted sediments, and the evolution of the seeps [17–28]. The seeps studied most in the OT are in its northern section (30.5°N-30.8°N) and were detected by R/V Kexue Yihao from July to August 2013 [18]. These unnamed seeps become the first group of targets of multidisciplinary research.
... The C 1 /C 2 and C 1 /C 3 ratios of the vent B samples were 445-1443 (mean 1096) and 889-1816 (mean 1567), respectively. The C 1 /(C 2 + C 3 ) ratio, which is often used (with d 13 C values) to identify methane sources (Horita and Berndt, 1999;Chen et al., 2016), was 132-305 (mean 202) and 296-788 (mean 642) for the vent A and the vent B samples, respectively. During storage, both C 1 /C 2 and C 1 / C 3 ratios generally increased over time, even though those of some vent A samples decreased (Fig. 1e,f). ...
... (b) Classification of methane sources using d 13 C and C 1 / C 2+ ratios. Boundaries were as suggested by Horita and Berndt (1999) and Chen et al. (2016). Blue arrow indicates effect of microbial oxidation on the d 13 C and C 1 / C 2+ ratios of alkanes, as suggested in previous studies. ...
Aerobic oxidation of short-chain alkanes was observed in gas samples from the Lutao intertidal hydrothermal vents in Taiwan, during storage at 20 °C for up to 29 months without adding bacterial strains and replenishing substrates. The carbon isotope fractionation factors (εC) of methane (C1), ethane (C2), and propane (C3), were calculated using the Rayleigh fractionation equation to be −37.1 ± 7.5‰, −14.8 ± 4.8‰, and −4.7 ± 5.2‰, respectively. The hydrogen isotope fractionation factor (εH) of methane was determined to be −281 ± 187‰. DNA sequencing of the 16S rRNA gene in the vent fluids suggests that aerobic oxidation is dominated by methanotrophs of the genera Methylomicrobium and Methylophaga, which use the ribulose monophosphate pathway (RuMP). The degrees of isotope fractionation (εC and εH values) herein are larger than previously reported values, possibly due to the limited O2 supply and low abundance of aerobic methane-oxidizing bacteria in the experiments. Since the fractionation factor of methane is higher than those of ethane and propane, the aerobic oxidation of thermogenic or microbial alkanes could produce a carbon isotope reversal, which is frequently noted as a trait of abiotic hydrocarbons. This work demonstrates that in addition to anaerobic microbial oxidation, aerobic oxidation with a low cell density can also produce significant isotope fractionation of alkanes in geological closed/semi-closed environments and open flow reaction systems that are characterized by moderate temperatures and a limited supply of substrates and O2; these environments include cold seeps, mud volcanoes, and low-temperature hydrothermal plumes/aquifers/reservoirs.
... CO 2 /H 2 S scatter plot of Fig. 5b. For CH 4 , part of the spread can also be justified by additional contributions from other sources/processes, including biogenic and thermogenic sources (e.g., low-and high-T organic matter decomposition) and/or abiotic methane formed by reaction other than (2) (e.g., via the Fischer Tropsch reaction) (Chen et al. 2016 and references therein). However, we cannot rule out the possibility that, for such minor components, part of the variability is due to sampling artefacts (e.g., O 2 entrainment, and consequent oxidation) and/or analytical/instrumental errors. ...
Ocean acidification is one of the most dramatic effects of the massive atmospheric release of anthropogenic carbon dioxide (CO2) that has occurred since the Industrial Revolution, although its effects on marine ecosystems are not well understood. Submarine volcanic hydrothermal fields have geochemical conditions that provide opportunities to characterise the effects of elevated levels of seawater CO2 on marine life in the field. Here, we review the geochemical aspects of shallow marine CO2-rich seeps worldwide, focusing on both gas composition and water chemistry. We then describe the geochemical effects of volcanic CO2 seepage on the overlying seawater column. We also present new geochemical data and the first synthesis of marine biological community changes from one of the best-studied marine CO2 seep sites in the world (off Vulcano Island, Sicily). In areas of intense bubbling, extremely high levels of pCO2 (> 10,000 μatm) result in low seawater pH (< 6) and undersaturation of aragonite and calcite in an area devoid of calcified organisms such as shelled molluscs and hard corals. Around 100–400 m away from the Vulcano seeps the geochemistry of the seawater becomes analogous to future ocean acidification conditions with dissolved carbon dioxide levels falling from 900 to 420 μatm as seawater pH rises from 7.6 to 8.0. Calcified species such as coralline algae and sea urchins fare increasingly well as sessile communities shift from domination by a few resilient species (such as uncalcified algae and polychaetes) to a diverse and complex community (including abundant calcified algae and sea urchins) as the seawater returns to ambient levels of CO2. Laboratory advances in our understanding of species sensitivity to high CO2 and low pH seawater, reveal how marine organisms react to simulated ocean acidification conditions (e.g., using energetic trade-offs for calcification, reproduction, growth and survival). Research at volcanic marine seeps, such as those off Vulcano, highlight consistent ecosystem responses to rising levels of seawater CO2, with the simplification of food webs, losses in functional diversity and reduced provisioning of goods and services for humans.
... A translucent polypropylene funnel connected to a silicon tubing was used to trap bubbling gases. Gas samples were collected in lowpermeability glass bottles with a volume of about 100 mL using the method described in Chen et al. (2016). A butyl stopper and an aluminum ring were used to seal the vial. ...
... A butyl stopper and an aluminum ring were used to seal the vial. Potential organic contamination inherited in tubing or tubing connection prior to sampling was removed by rinsing with nitric acid (Chen et al., 2016). The temperatures of the emanated spring water were measured using a thermocouple with an accuracy of ±0.1°C. ...
... The O 2 was principally a contaminant from air during sampling, preservation, or analyzing (Chen et al., 2016). We used the aircorrection methods as follow: ...
The Tengchong volcanic field, located at the collision zone between the Indian and Eurasian plates, is well known for its large-scale Holocene volcanic eruptions and extensive hydrothermal activities. Bubbling gases from eight geothermal springs at the Tengchong field were collected and analyzed for their chemical and isotopic compositions (³He/⁴He, ²⁰Ne, N2, Ar, δ¹³CCH4 and δ¹³CCO2). The results show that the gas samples could be categorized into a group I dominated by N2 and a group II with CO2 as major component. The air-corrected ³He/⁴He ratios ranged from 0.17 Ra to 4.76 Ra and the calculated mantle contributions dramatically varied from 1.9% to 77.9% for group II. By contrast, an invariant air-corrected ³He/⁴He ratio of about 0.30 Ra and a relatively constant mantle contribution of 4.0% to 5.0% was obtained for group I. The sampling sites just on top of the magma chamber received significant mantle-derived helium and magmatic gas components (at the proximal site of the magma chamber: >95% magmatic gas contributions). The calculated N2/Ar ratio of the hydrothermal endmember for group II (sample sites close to the magma chamber) was 61.7–66.2, suggesting that the reaction zone temperature is between 223 °C and 252 °C. The influence of the magma chamber decreases with increasing distance of the sampling sites from the chamber apex. The sampling sites (group I) at the marginal area discharge gases with relatively low ³He/⁴He ratios and magmatic contributions (19–24%). The temperature of the reaction zone for this group was estimated to be 74 °C based on the N2/Ar ratio of 42. This study provided important constraints to relate hydrothermal gas geochemistry directly with the spatial distribution of the underlying magma chamber.
Plain language summary
Geochemical characteristics of gases discharged from hydrothermal systems are usually affected by deep magmatic processes, shallow hot fluids circulation, and water-rock interactions in the reaction zone. In this study, we analyzed the gas abundances and isotopic compositions of hydrothermal gas discharged from the Yunnan-Tibet geothermal belt. We used a gas mixing model to quantify the contributions of mantle-derived/magmatic endmember and hydrothermal endmember. The ³He/⁴He ratios, magmatic contribution, and temperature of the reaction zone decreased significantly with increasing distance from the magma chamber underneath the Tengchong field, highlighting the intimate relationships between gas transport, hydrothermal circulation and the extent of the magma chamber.
... Kueishantao, located between the Okinawa Trough and the Philippines basin, hosts recent magmatic activity attributed to extension of the Okinawa Trough, with the most recent eruption dated around 7 ka (Chen et al., 2001). Hydrothermal venting is well-studied (e.g., Chen et al., 2005;Yang et al., 2012;Chen et al., 2016;Lin et al., 2019), and is associated with highly acidic fluids (pH~2.5-3) venting at temperatures of up to~120°C and with free gases, mainly CO 2 (Chen et al., 2005;Chen et al., 2016). ...
... Hydrothermal venting is well-studied (e.g., Chen et al., 2005;Yang et al., 2012;Chen et al., 2016;Lin et al., 2019), and is associated with highly acidic fluids (pH~2.5-3) venting at temperatures of up to~120°C and with free gases, mainly CO 2 (Chen et al., 2005;Chen et al., 2016). These plumes are also particle-rich, discharging whitish and yellow fluids, depending on the concentration of sulfur particles (Chen et al., 2001;Han et al., 2014). ...
... These plumes are also particle-rich, discharging whitish and yellow fluids, depending on the concentration of sulfur particles (Chen et al., 2001;Han et al., 2014). Gas geochemistry indicate both magmatic degassing and interaction of fluids with marine sediments at depth (Chen et al., 2016), and likely indicate a magmatic system located beneath this island, as indicated by recent seismic studies (Lin et al., 2018). This area is seismically active, owing to both the underlying subduction and intra-arc extension (e.g., Lin et al., 2018), and a possible 2005 diking event associated with the Ilan earthquake (Lai et al., 2009). ...
We investigate the potential of satellite imagery to map and monitor the activity of shallow-water hydrothermal systems, which are often found around volcanic islands. For this study, we used publicly available data and proprietary WorldView-2 satellites images, with spectral bands that can penetrate up to water depths of 30 m. Shallow water hydrothermal sites are visible on satellite imagery, primarily with publicly available data, demonstrating the potential of satellite imagery to study and monitor shallow water hydrothermal activity. We focus our work on volcanic islands, showing intense near-shore, shallow-water hydrothermal activity, and distinct styles of hydrothermal venting. Satellite imagery constrains regional outflow geometry and the temporal variability or stability of these systems. Milos Island shows hydrothermal outflow associated with reflective mineral precipitates and/or bacterial mats, which are stable over time (2010-2014). These outflows locally define polygonal patterns likely associated with hydrothermal convection in porous media. In Kueishantao Island individual hydrothermal plumes charged with particles are visible at the sea surface, and display great variability in intensity and distribution of plume sources (2002-2019). Worldwide we have identified ~15 shallow water hydrothermal sites with satellite imagery, that are similar to either the Milos system (e.g., Vulcano and Panarea, Italy), or the Kueishantao system (numerous sites in Pacific volcanic islands). This study demonstrates that satellite imagery can be used to map and monitor different types of shallow-water hydrothermal systems, at regional scale, and monitor their evolution. Satellite data provide not only regional and temporal information on these systems, unavailable to date, but also the regional context for follow-up in situ field data and observations (e.g., instrumental monitoring, sampling, observations and mapping with divers or AUVs) to understand both the nature and dynamics of these systems, and ultimately the associated fluxes.
... Submarine hydrothermal activities have been reported at various locations off the southeast coast of the islet . The region has undergone extensive geochemical investigations that characterize the composition and distribution of gases Chen et al., 2016), dissolved species (Yang et al., 2012;Chen et al., 2018), and sediment (Hung et al., 2018;Yu et al., 2019). The suspended particles have also been examined, but mainly from the perspective of microbial community composition and functionality (Zhang et al., 2012;Tang et al., 2013Tang et al., , 2018Li et al., 2018) and partly for food web reconstruction (Chang et al., 2018). ...
The particulate organic matter (POM) of shallow-water hydrothermal fields has been studied in the context of food web reconstruction, but the processes governing its biogeochemistry and dynamics are poorly explored. Here, we investigate the POM in the Kueishantao hydrothermal field using chemical and hydrodynamic approaches. The depletion of total suspended matter, lower C/N ratios, and higher carbon isotopic values of particulate organic carbon (δ13CPOC) in the vertical plumes relative to values derived from Si-based models were attributed to the hydraulic sorting of the vented particles, which tend to have more N and 13C in the fine fraction. The particulate organic carbon (POC), unlike the total suspended matter, was enriched in the vertical plumes and explained by physicochemical processes rather than biological addition. The POC-enriched plume-top water was found to be a better endmember than the vent fluids to explain particle mixing in the lateral plume. Physical mixing played a steering role in shaping the particle chemistry of the lateral plumes, but markedly 13C-enriched POC was still observable in several near-vent, low-to-intermediate-Si plume waters, implying locally enhanced primary production of at least 0.1–0.4 mg C/m3/h. The presence of eddies, confirmed by flow field measurements, should have contributed to the detection of biogeochemical anomalies via extending the retention time of plume water to 1–2 h. The dominating mixing process resulted in decoupling between the δ13CPOC signatures and carbonate chemistry in this shallow-water hydrothermal plume.
