[en] The geological units in Shandong Province, North China are important parts of the North China Craton and offer important insights into their crustal evolutionary history. This work compiled 611 sets of Nd isotopic data of Archean-Mesozoic rocks from Shandong including the Luxi, Jiaobei, and Sulu terranes, which provided important constraints for crustal growth and reactivation. Nd-depleted mantle model ages (T_DM) of Archean rocks with positive ε_Nd(t) values showed that ca. 2.9 and 2.8-2.7 Ga were the most important periods of crustal growth in the Jiaobei and Luxi terranes, respectively, while the period of ca. 2.6-2.5 Ga in the Jiaobei terrane likely indicated a coherent event of crustal growth and reworking. During the Proterozoic, multi-stage rifting and collisional orogenic events possibly led to the reworking of Archean crust in the source region. The Nd isotopic data of the Paleoproterozoic and Neoproterozoic rocks from Sulu indicated significant reworking of older crust with juvenile magmatic input. Crustal reactivation occurred during the Mesozoic. The younger T_DM ages of the Mesozoic rocks with low negative ε_Nd(t) values indicated that a juvenile crustal/mantle component was added to the ancient basement. The reactivation reflected significant crust-mantle interaction via the mechanism of crustal subduction and mantle-derived magma un-derplating, or possibly asthenospheric upwelling. Our work also attempted to establish the crustal correlation between Shandong and Korea (including the Gyeonggi massif, Ogcheon belt, and Yeongnam massif). The T_DM age distribution provided evidence favoring the affinity relationship between the Gyeonggi massif and Ogcheon belt of South Korea and the Jiaobei and Sulu terranes of Shandong, while the Yeongnam massif was more correlated with the South China Block.

[en] Highlights: • Chl-α presented higher influence on the northern communities. • SST and upwelling influenced the southern communities. • Latitudinal gradient given by the SST was the main driver for community functioning. • High species richness and functional redundancy suggested community resilience. There is limited understanding on nearshore fish community functioning in relation to changing environmental gradients. To address this, we investigated the trait composition of fish communities in five regions along the Portuguese coast during 4 years. Northern regions were characterized by higher Chlorophyll-α and small-sized species with short lifespans. The southernmost region was characterized by warmer waters, more intense upwelling events and typical warm-water species. Higher species richness and functional redundancy at the southernmost region suggested that in case of potential species loss, community functioning would be less affected in this region, and thus, a certain level of community resilience is maintained. The central region presented lower functional redundancy and high functional richness, which indicated the presence of rare species with rare traits, suggesting a more vulnerable community. This information on the nearshore fish community distribution may be particularly important towards managing coastal ecosystems in response to changing environmental conditions.

[en] In this study we investigate the possible reasons for the widespread differences between the seasonal cycles of carbon production and export compared to those of hypoxia in eastern boundary upwelling systems. An idealized model is proposed that qualitatively characterizes the relative roles of physics and biogeochemical fluxes. The model is tested on three contrasting upwelling systems: the Benguela (from relatively aerated to interannual anoxic), the Humboldt (sub-oxic and interannually anoxic) and the Cariaco (permanently anoxic). Overall we propose that shelf hypoxia variability can be explained on the basis of the interaction between ventilation by ocean boundary forcing through ocean-shelf exchange and the role of shelf geometry in the retention of shelf-based particulate organic carbon (POC) fluxes. We aim to identify the hypoxia regimes associated with low ventilation-wide-shelf systems and high ventilation-narrow-shelf systems, considering them as extremes of conditions controlled by the two factors. We propose that this may help to explain differences in the seasonal cycles of the biogeochemical drivers and responses as well as difference between upwelling systems and within individual upwelling systems. It is suggested that when seasonal hypoxia emerges it does so preferentially at a wide-shelf part of a system.

[en] Highlights: • Bacterioplankton and microeukaryotes showed differential responses to upwelling. • Upwelling altered microbial eukaryotic communities and decreased their diversity. • Upwelling increased populations of diatoms and thraustochytrids in surface waters. • Temperature was the most important environmental factor of community structure. Upwelling plays an important role in marine ecosystems and potentially reshapes microbial communities by enhanced dispersal and distinct environmental drivers. Relative to that of bacterioplankton, however, the response of eukaryotic microbes to upwelling is largely unknown. Here, we investigated the influence of coastal upwelling in South China Sea on the microbial eukaryotic communities. Unlike several folds of increase in the cell abundance of bacterioplankton in upwelling than non-upwelling stations at corresponding water layers, no significant difference was detected for the total microbial eukaryotic 18S rRNA gene abundance. Moreover, the microbial eukaryotes in the upwelling stations exhibited increasing 18S rRNA gene abundance from the surface to the deep, contrasting the vertical cell abundance pattern of the bacterioplankton; but their vertical abundance patterns were similar in non-upwelling stations. Importantly, the coastal upwelling significantly reduced the community evenness of the microbial eukaryotes and slightly reduced their Shannon diversity. Their community composition also varied obviously especially between the surface waters of upwelling and non-upwelling stations. Among the dominant supergroups, Alveolata was found to be less abundant while Stramenopiles, particularly thraustochytrids and diatoms, to be more abundant in the surface water of upwelling than non-upwelling stations. Temperature was identified as the most important factor of the microbial eukaryotic community composition, suggesting potential effects of the cold upwelling water masses on specific taxa. Overall, our results reveal significant and distinct impacts of coastal upwelling on the abundance, diversity, and community structure of microbial eukaryotes, filling the knowledge gap about the microbial responses to this important marine phenomenon.

[en] The upper-oceanic response to a moving typhoon, and the mechanism of the response, are studied based on linear theory and a numerical experiment. The results of the analysis by linear theory are summarized as follows. Three different processes (Ekman pumping, inertial pumping and 'anti-Ekman' pumping) contribute to the upper-oceanic vertical motions caused by a moving atmospheric disturbance. The dominant process depends on the Coriolis parameter f, the moving speed U of the disturbance and the along-track wavenumber spectrum of the wind stress curl. In the case of a typhoon, when the wavenumber spectrum has a dominant amplitude at k< f/U, Ekman pumping is the dominant mechanism and upwelling occurs at the typhoon center, where k is the along-track wavenumber. When the wavenumber spectrum has a significant amplitude near k∼f/U, inertial pumping is dominant and upwelling occurs to the rear of the typhoon center. The results of the numerical experiments show that linear theory performs well in explaining the horizontal structures of the upper-oceanic vertical motions and their dependence on the moving speed of the typhoon.

[en] Highlights: • Coral Symbiodiniaceae density (SD) shows intergeneric and spatial differences. • Corals with high SD in South China Sea (SCS) have stronger thermal tolerance. • Corals at outer reef slope of SCS atoll possess higher SDs than those at lagoon. • Corals in SCS Huangyan Atoll have higher SDs than those at neighboring reefs. • Human disturbances may limit the function of potential refuges for SCS corals. The healthy status of corals in the isolated atolls of the central South China Sea (SCS) remains unclear. Symbiodiniaceae density (SD) can effectively reflect the thermal tolerance and health of hard corals. Here, the SDs of 238 samples from the Huangyan Atoll (HA) were analyzed. The results revealed significantly intergeneric and geomorphological differences in SD. Intergeneric variation may reflect that corals with high SD have stronger thermal tolerance. Geomorphic analysis showed that the SDs at the outer reef slope were higher than in the lagoon. Hydrodynamics and sea surface temperature were likely the main influencing factors. Most notably, corals in SCS HA had higher SDs than those at neighboring reefs, indicating that their thermal tolerance were strong, which may be related to HA's local upwelling. These results suggest that the HA has the potential to serve as a refuge for corals, but increasing human disturbance limit its function.

[en] To constrain the accurate age of a marine sediment record, the radiocarbon (14C) ages need to be corrected for short-term and small-scale changes in planktic 14C reservoir ages (Rplank). Nevertheless, accurate records of past changes in Rplank are scarce. Here we present a high-resolution record of deglacial 14C ages measured on Globigerina bulloides in sediment core M77/2-59-1 from the northern boundary (~4°S, 997 m) of the Peruvian upwelling zone. The fine structure of jumps and plateau boundaries in the 14C record were tuned to synchronous, thus global structures in the atmospheric 14C record of Lake Suigetsu (Bronk Ramsey et al., 2012) and used as tie points for an age model with semi-millennial resolution, moreover to reconstruct deglacial changes in Rplank from 17 to 11 cal. ka. In our record, Rplank drops from 1250 14C yr prior to 14 cal. ka to ~600 – 450 14C yr until the plateau named Top of Younger Dryas. The drop suggests a major decrease in coastal upwelling, possibly the result of a southward (poleward) expansion of the Intertropical Convergence Zone and related shift in the southeastern trade wind belt during the Bølling-Allerød. Subsequent to 14 cal. ka our Rplank values are roughly similar to values obtained for thermocline waters near the equator from the age difference between 14C ages of wood chunks and 14C of G. ruber (Zhao & Keigwin, 2018). Prior to 14 cal. ka our Rplank are ~800 14C yr higher, which corroborates the presumed latitudinal shift of coastal upwelling. Our 14C ages measured on G. bulloides differ in part from paired 14C ages of Neogloboquadrina dutertrei, indicating their habitat in different water masses prior to 14 cal. ka, in support of the upwelling affinity of G. bulloides. In addition, we used our Rplank values to accurately derive past ventilation ages of intermediate waters near 1000 m depth based on the difference of paired benthic and planktic 14C ages, which is important to constrain centennial to millennial scale changes in circulation influencing the extent of the Peruvian oxygen minimum zone. References: Bronk Ramsey, C., et al., Science, 338, 370–374, 2012. Zhao & Keigwin, Nature communications, 9, 3077, 2018.

[en] Decreased ventilation of the Southern Ocean in glacial time is implicated in most explanations of lower glacial atmospheric CO₂. Today, the deep (>2000 m) ocean south of the Polar Front is rapidly ventilated from below, with the interaction of deep currents with topography driving high mixing rates well up into the water column. We show from a buoyancy budget that mixing rates are high in all the deep waters of the Southern Ocean. Between the surface and 2000 m depth, water is upwelled by a residual meridional overturning that is directly linked to buoyancy fluxes through the ocean surface. Combined with the rapid deep mixing, this upwelling serves to return deep water to the surface on a short time scale. We propose two new mechanisms by which, in glacial time, the deep Southern Ocean may have been more isolated from the surface. Firstly, the deep ocean appears to have been more stratified because of denser bottom water resulting from intense sea ice formation near Antarctica. The greater stratification would have slowed the deep mixing. Secondly, subzero atmospheric temperatures may have meant that the present-day buoyancy flux from the atmosphere to the ocean surface was reduced or reversed. This in turn would have reduced or eliminated the upwelling (contrary to a common assumption, upwelling is not solely a function of the wind stress but is coupled to the air/sea buoyancy flux too). The observed very close link between Antarctic temperatures and atmospheric CO₂ could then be explained as a natural consequence of the connection between the air/sea buoyancy flux and upwelling in the Southern Ocean, if slower ventilation of the Southern Ocean led to lower atmospheric CO₂. Here we use a box model, similar to those of previous authors, to show that weaker mixing and reduced upwelling in the Southern Ocean can explain the low glacial atmospheric CO₂ in such a formulation

[en] A new three-band model was developed to estimate chlorophyll-a concentrations in turbid inland waters. This model makes a number of important improvements with respect to the three-band model commonly used, including lower restrictions on wavelength optimization and the use of coefficients which represent specific inherent optical properties. Results showed that the new model provides a significantly higher determination coefficient and lower root mean squared error (RMSE) with respect to the original model for upwelling data from Taihu Lake, China. The new model was tested using simulated data for the MERIS and GOCI satellite systems, showing high correlations with the former and poorer correlations with the latter, principally due to the lack of a 709 nm centered waveband. The new model provides numerous advantages, making it a suitable alternative for chlorophyll-a estimations in turbid and eutrophic waters.

[en] Behavior and teleconnections associated with canonical El Niño (~ 18–24 months; CE) and protracted El Niño (> greater than 3 years; PE) events are revisited in the present study. A careful look at seasonal mean of SST anomalies averaged over Niño3.4 region for the period 1980–2010 shows that El Niño episodes in the boreal winter of 1991 and 2002 do not turn into La Niña as CE events (1982–1983, 1986–1988, 1997–1998, 2009–2010). Unlike phase transition in canonical cases of El Niño followed by a neutral or La Niña event, El Niño episodes in the years 1991 and 2002 continued as weak El Niño for another 3 years. A typical signature of CE events in the tropical Indian Ocean (IO) is basin-wide warming, whereas in the case of PE events, warming remains highly localized and relatively weaker in magnitude. PE events are found to be associated with almost no subsurface ocean propagation in the equatorial Pacific Ocean (PO). PE events are linked to more frequent westerly wind bursts (WWBs) of weaker intensity and smaller timespan compared to CE cases. Strong IO warming during CE events generates easterlies in the equatorial western PO, which extend further towards the eastern PO as upwelling Kelvin waves. This upwelling Kelvin waves shoals thermocline through Ekman divergence and cools the sea surface temperature (SST) during the decay phase of El Niño. During PE cases, localized IO warming is incapable of generating significant atmospheric response in the form of easterlies and therefore frequent WWBs help in maintaining positive SST anomalies in the eastern PO.