scholarly journals Provenance of tetraether membrane lipids in a large temperate lake (Loch Lomond, UK): implications for glycerol dialkyl glycerol tetraether (GDGT)-based palaeothermometry

2014 ◽  
Vol 11 (19) ◽  
pp. 5539-5563 ◽  
Author(s):  
L. K. Buckles ◽  
J. W. H. Weijers ◽  
X.-M. Tran ◽  
S. Waldron ◽  
J. S. Sinninghe Damsté
Keyword(s):  
Lake Sediments ◽  
Water Column ◽  
Membrane Lipids ◽  
Lacustrine Sediments ◽  
Small Rivers ◽  
The South ◽  
Factors Affecting ◽  
The North ◽  
Loch Lomond

Abstract. The application of glycerol dialkyl glycerol tetraether (GDGT)-based palaeoenvironmental proxies, such as the branched vs. isoprenoidal tetratether (BIT) index, TEX86 and the MBT–CBT palaeothermometer, has lately been expanded to lacustrine sediments. Given recent research identifying the production of branched, bacterial GDGTs (brGDGTs) within lakes, it is necessary to ascertain the effect of this lacustrine production on GDGT-based proxies. This study profiles a temperate, monomictic lake (Loch Lomond, UK), analysing labile intact polar GDGT lipids (IPLs) and resilient core GDGT lipids (CLs) in catchment soils, small tributary rivers, lake water and lake sediments. Loch Lomond consists of two basins bisected by the Highland Boundary Fault, resulting in a mesotrophic to oligotrophic gradient from south to north. The north basin is fjord-like, while the south basin is shallow with a lowland catchment. Besides abundant influxes of allochthonous soil- and peat-derived (CL) brGDGTs, brGDGTs are produced in a variety of settings in Loch Lomond. Rather than integrating a scattered soil signal, there is some evidence that small rivers may contribute to the brGDGT pool through addition of brGDGTs produced in situ in these streams. Three hundred days of settling particles and water column profiles of suspended particulate matter (SPM; March and September 2011) reveal brGDGT production throughout the water column, with (IPL and CL) brGDGT distributions varying by basin. In lake sediments, in situ brGDGT production affects the distributions of sedimentary brGDGTs despite high soil- and peat-derived organic matter influxes from the catchment. MBT–CBT-derived mean annual air temperature (MAAT) estimates from soil, river and lake sediments vary widely. A strong bias towards higher MAATs in the south and lower MAATs in the north basin further complicates the application of the proxy. These results emphasise that caution must be exercised when applying the MBT–CBT palaeothermometer to individual lakes in which the use of the proxy has not been validated and therefore the factors affecting its application are not well understood. Despite elevated BIT indices, (partly) due to in situ brGDGT production, reliable TEX86 lake surface temperature (LST) estimates were obtained from SPM with BIT indices up to 0.9. Lower north basin sediments yielded accurate LST estimates but require further evaluation to properly constrain the application of the TEX86 proxy.

scholarly journals Provenance of tetraether membrane lipids in a large temperate lake (Loch Lomond, UK): implications for GDGT-based palaeothermometry

2014 ◽  
Vol 11 (3) ◽  
pp. 4187-4250 ◽  
Author(s):  
L. K. Buckles ◽  
J. W. H. Weijers ◽  
X.-M. Tran ◽  
S. Waldron ◽  
J. S. Sinninghe Damsté
Keyword(s):  
Lake Sediments ◽  
Water Column ◽  
Membrane Lipids ◽  
Lacustrine Sediments ◽  
Small Rivers ◽  
The South ◽  
Factors Affecting ◽  
The North ◽  
Loch Lomond

Abstract. The application of glycerol dialkyl glycerol tetraether (GDGT)-based palaeoenvironmental proxies, such as the BIT index, TEX86 and the MBT/CBT palaeothermometer, has lately been expanded to lacustrine sediments. Given recent research identifying the production of branched, bacterial GDGTs (brGDGTs) within lakes, it is necessary to ascertain the effect of this lacustrine production on GDGT-based proxies. This study profiles a temperate, monomictic lake (Loch Lomond, UK), analysing labile intact polar GDGT lipids (IPLs) and resilient core GDGT lipids (CLs) in catchment soils, small tributary rivers, lake water and lake sediments. Loch Lomond consists of two basins bisected by the Highland Boundary Fault, resulting in a mesotrophic to oligotrophic gradient from south to north. The north basin is fjord-like, while the south basin is shallow with a lowland catchment. Besides abundant influxes of allochthonous soil and peat-derived (CL) brGDGTs, brGDGTs are produced in a variety of settings in Loch Lomond. Rather than integrating a scattered soil signal, there is some evidence that small rivers may contribute to the brGDGT pool through addition of brGDGTs produced in situ in these streams. 300 days of settling particles and water column profiles of suspended particulate matter (SPM; March and September 2011) reveal brGDGT production throughout the water column, with (IPL and CL) brGDGT distributions varying by basin. In lake sediments, in situ brGDGT production affects the distributions of sedimentary brGDGTs despite high soil and peat-derived organic matter influxes from the catchment. MBT/CBT-derived mean annual air temperature (MAAT) estimates from soil, river and lake sediments vary widely. A strong bias towards higher MAATs in the south and lower MAATs in the north basin further complicates the application of the proxy. These results emphasise that caution must be exercised when applying the MBT/CBT palaeothermometer to individual lakes in which the use of the proxy has not been validated and therefore the factors affecting its application are not well understood. Despite elevated BIT indices, (partly) due to in situ brGDGT production, reliable TEX86 lake surface temperature (LST) estimates were obtained from SPM with BIT indices up to 0.9 but containing abundant crenarchaeol. Lower north basin sediments yielded accurate LST estimates but require further evaluation to properly constrain the application of the TEX86 proxy.

scholarly journals A 900-year New England temperature reconstruction from <i>in situ</i> seasonally produced branched glycerol dialkyl glycerol tetraethers (brGDGTs)

2018 ◽  
Author(s):  
Daniel R. Miller ◽  
M. Helen Habicht ◽  
Benjamin A. Keisling ◽  
Isla S. Castañeda ◽  
Raymond S. Bradley
Keyword(s):  
New England ◽  
Water Column ◽  
Lacustrine Sediments ◽  
Temperature Reconstruction ◽  
Early Spring ◽  
Pollen Record ◽  
The North ◽  
The North Atlantic Oscillation ◽  
Glycerol Dialkyl Glycerol Tetraethers

Abstract. Paleotemperature reconstructions are essential for distinguishing anthropogenic climate change from natural variability. An emerging method in paleoclimatology is the use of branched glycerol dialkyl glycerol tetraethers (brGDGTs) in lacustrine sediments to reconstruct temperature, but their application is hindered by a limited understanding of their sources, seasonal production, and transport. We report seasonally resolved measurements of brGDGT production within the water column, in catchment soils and in a sediment sequence from a small, deep inland lake in Maine, USA. BrGDGT distributions in the water column are distinct from catchment soils but similar to the distributions in lake sediments, suggesting that (1) brGDGTs are produced within the lake and (2) this in situ production dominates the downcore sedimentary signal. Seasonally, depth-resolved measurements indicate that the dominant production of brGDGTs occurs in late fall/early spring and at intermediate depths (18–30 meters) in the water column. We apply these observations to help interpret a 900-year-long brGDGT-based temperature reconstruction and find that it shows similar trends to a pollen record from the same site and to regional and global syntheses of terrestrial temperatures over the last millennium. However, the record also shows higher-frequency variability than has previously been captured by such an archive in the Northeastern United States, potentially attributed to the North Atlantic Oscillation and volcanic/solar activity. This is the first brGDGT- based multi-centennial paleoreconstruction from this region and contributes to our understanding of the production and fate of brGDGTs in lacustrine systems.

The Earliest Ceramics of the Northern Maya Lowlands

2018 ◽  
Author(s):  
E. Wyllys Andrews V ◽  
George J. Bey ◽  
Christopher M. Gunn
Keyword(s):  
The South ◽  
Maya Lowlands ◽  
The North

This chapter examines the evidence for pre-Mamom pottery in the northern Maya lowlands. This pottery, recognized as the Ek complex, has been identified at Komchen and Kiuic as well as several other sites in the western part of northern Yucatan. The identification, description, and comparison of this pottery with contemporary complexes from the southern Maya lowlands establishes Ek pottery as the oldest ceramic complex (900-800 B.C.) recovered in the north. Northern Maya culture is thought to be the result of a process of in situ evolution which begins at roughly the same time it happened in the south.

Understanding Societies in War

2018 ◽  
Author(s):  
Paul D. Escott
Keyword(s):  
Ethnic Groups ◽  
Irregular Warfare ◽  
The South ◽  
Factors Affecting ◽  
The North ◽  
Role Of Women ◽  
Democratic Parties ◽  
The Impact

This chapter emphasizes the analysis of the wartime forces in both sections that affected unity or division. It raises questions about the roots of the large amount of internal violence or irregular warfare in the South. For the North, it probes the nature of nationalism and asks about that section’s social, political, and religious divisions. Factors affecting both the Republican and the Democratic Parties of the North deserve new attention, as do the role of women in both sections, ethnic groups in the North especially, and the impact of emancipation and racism.

scholarly journals Position and structure of the Subtropical/Azores Front region from combined Lagrangian and remote sensing (IR/altimeter/SeaWiFS) measurements

1999 ◽  
Vol 79 (5) ◽  
pp. 769-792 ◽  
Author(s):  
Robin D. Pingree ◽  
Carlos Garcia-Soto ◽  
Bablu Sinha
Keyword(s):  
Remote Sensing ◽  
Far East ◽  
The South ◽  
Subtropical Front ◽  
The North ◽  
Mid Atlantic Ridge ◽  
Temperature Contrast ◽  
Front Region ◽  
Lagrangian Flow

The position and structure of the North Atlantic Subtropical Front is studied using Lagrangian flow tracks and remote sensing (AVHRR imagery: TOPEX/POSEIDON altimetry: SeaWiFS) in a broad region (∼31° to ∼36°N) of marked gradient of dynamic height (Azores Current) that extends from the Mid-Atlantic Ridge (MAR), near ∼40°W, to the Eastern Boundary (∼10°W). Drogued Argos buoy and ALACE tracks are superposed on infrared satellite images in the Subtropical Front region. Cold (cyclonic) structures, called ‘Storms’, and warm (anticyclonic) structures of 100–300 km in size can be found on the south side of the Subtropical Front outcrop, which has a temperature contrast of about 1°C that can be followed for ∼2500 km near 35°N. Warmer water adjacent to the outcrop is flowing eastward (Azores Current) but some warm water is returned westward about 300 km to the south (southern Counterflow). Estimates of horizontal diffusion in a Storm (D=2.2×102 m2 s−1) and in the Subtropical Front region near 200 m depth (Dx=1.3×104 m2 s−1, Dy=2.6×103 m2 s−1) are made from the Lagrangian tracks. Altimeter and in situ measurements show that Storms track westwards. Storms are separated by about 510 km and move westward at 2.7 km d−1. Remote sensing reveals that some initial structures start evolving as far east as 23°W but are more organized near 29°W and therefore Storms are about 1 year old when they reach the MAR (having travelled a distance of 1000 km). Structure and seasonality in SeaWiFS data in the region is examined.

scholarly journals The stratigraphy of the Neogene-Quaternary succession in the southwest Netherlands from the Schelphoek borehole (42G4-11/42G0022) – a sequence-stratigraphic approach

2007 ◽  
Vol 86 (4) ◽  
pp. 317-332 ◽  
Author(s):  
A.A. Slupik ◽  
F.P. Wesselingh ◽  
A.C. Janse ◽  
J.W.F. Reumer
Keyword(s):  
The Netherlands ◽  
Coastal Area ◽  
Late Quaternary ◽  
Tidal Channel ◽  
The South ◽  
Glacial Cycles ◽  
Sequence Stratigraphic ◽  
The North ◽  
Mammal Fauna

AbstractWe investigate the stratigraphy of Neogene and Quaternary intervals of the Schelphoek borehole (Schouwen, Zeeland, the Netherlands). The Breda Formation (Miocene-Zanclean) contains three sequences separated by hiatuses. The Oosterhout Formation (Zanclean-Piacenzian) contains at least two sequences. This formation is overlain by seven sequences of the Gelasian Maassluis Formation that almost certainly represent glacial cycles. The three lowermost sequences are provisionally assigned to the Praetiglian (MIS 96, MIS 98 and MIS 100). A large hiatus exists between the top of the Maassluis Formation and the base of the late Middle to Late Quaternary succession. Due to extensivein situreworking of older strata (including fossils) at the base of several of the formations, their exact boundaries are difficult to establish. The Neogene succession in the Schelphoek borehole is compared to the stratigraphic successions in the Antwerp area to the south and the Dutch coastal area and continental platform to the north. Finally, the stratigraphic context of the Gelasian (‘Tiglian’) mammal fauna dredged from the bottom of a major tidal channel in the adjacent Oosterschelde is assessed by comparison with the Schelphoek borehole.

In-situ investigation of alkalinity - denitrification coupling in the sediment - water column interface

2020 ◽  
Author(s):  
Mona Norbisrath
Keyword(s):  
Water Column ◽  
German Bight ◽  
Anthropogenic Impacts ◽  
Binding Capacity ◽  
Quantitative Relationship ◽  
Terminal Electron Acceptor ◽  
The North ◽  
In Situ Investigation ◽  
In Situ Experiments

&lt;p&gt;&lt;strong&gt;Abstract: EGU 2020&lt;/strong&gt;&lt;/p&gt;&lt;p&gt;&lt;strong&gt;Session: BG4.1: Biogeochemistry of coastal seas and continental shelves (Helmuth Thomas)&lt;/strong&gt;&lt;/p&gt;&lt;p&gt;Mona Norbisrath&lt;sup&gt;1&lt;/sup&gt;, Kirstin D&amp;#228;hnke&lt;sup&gt;1&lt;/sup&gt;, Andreas Neumann&lt;sup&gt;1&lt;/sup&gt;, Justus van Beusekom&lt;sup&gt;1&lt;/sup&gt;, Nele Treblin&lt;sup&gt;1&lt;/sup&gt;, Bryce van Dam&lt;sup&gt;1&lt;/sup&gt;, Helmuth Thomas&lt;sup&gt;1&lt;/sup&gt;&lt;/p&gt;&lt;p&gt;&lt;sup&gt;1&lt;/sup&gt;Institute for Coastal Research, Helmholtz-Zentrum Geesthacht&lt;/p&gt;&lt;p&gt;Contact: [email protected]&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;&lt;strong&gt;In-situ investigation of alkalinity - denitrification coupling in the sediment - water column interface&lt;/strong&gt;&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;As a shallow shelf sea, the North Sea is very vulnerable to anthropogenic impacts like rising CO&lt;sub&gt;2&lt;/sub&gt; concentrations, increasing nutrient inflows and coincident oxygen loss.&lt;/p&gt;&lt;p&gt;Two important processes that determine the role of the coastal ocean as a net sink for anthropogenic CO&lt;sub&gt;2&lt;/sub&gt; are alkalinity and denitrification. Alkalinity, the acid binding capacity of the ocean, buffers natural and anthropogenic changes in the oceans&amp;#8217; CO&lt;sub&gt;2&lt;/sub&gt; and pH system. Denitrification, an anaerobic microbial process in which organic matter is respired, uses NO&lt;sub&gt;3&lt;/sub&gt;&lt;sup&gt;-&lt;/sup&gt; instead of O&lt;sub&gt;2&lt;/sub&gt; as a terminal electron acceptor. Denitrification reduces NO&lt;sub&gt;3&lt;/sub&gt;&lt;sup&gt;-&lt;/sup&gt; to N&lt;sub&gt;2&lt;/sub&gt; and in turn produces alkalinity.&lt;/p&gt;&lt;p&gt;Eutrophication, caused by leaching of excess fertilizer nutrients into coastal seas, leads to enhanced denitrification and therefore to enhanced alkalinity as well as an increased uptake of CO&lt;sub&gt;2&lt;/sub&gt;. However, the quantitative relationship between denitrification and alkalinity production and its control under changing environmental conditions is yet to be determined.&lt;/p&gt;&lt;p&gt;In the German Bight, denitrification is usually restricted to anoxic sediments. In this study, we therefore focus on in-situ experiments in the sediment - water column interface. Batch core incubations in combination with the isotope pairing technique (IPT) and labelled nitrate additions were used to detect denitrification and gauge its effect on alkalinity production during a cruise on RV Heincke (HE541) in September 2019 in the German Bight. To quantify denitrification, the production of all three N&lt;sub&gt;2&lt;/sub&gt; isotope species (&lt;sup&gt;28&lt;/sup&gt;N&lt;sub&gt;2&lt;/sub&gt;, &lt;sup&gt;29&lt;/sup&gt;N&lt;sub&gt;2&lt;/sub&gt; and &lt;sup&gt;30&lt;/sup&gt;N&lt;sub&gt;2&lt;/sub&gt;) is measured using a membrane inlet mass spectrometer (MIMS). We expect an increase of denitrification rates with nitrate concentrations and incubation times, and we will quantify benthic denitrification. We will further evaluate the assumption of concurrent increases in alkalinity production and will investigate the benthic-pelagic coupling of these processes. Investigating the in-situ interaction of metabolic alkalinity and denitrification will give an estimation of the alkalinity impact on the reduction of anthropogenic CO&lt;sub&gt;2&lt;/sub&gt; in the atmosphere.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;

The waterbodies of the Dallol volcano: A physico-chemical and geo-microbial survey

2020 ◽  
Author(s):  
Hugo Moors ◽  
Miroslav Honty ◽  
Carla Smolders ◽  
Ann Provoost ◽  
Mieke De Craen ◽  
...  
Keyword(s):  
Saline Water ◽  
Halophilic Archaea ◽  
Mining Area ◽  
Ex Situ ◽  
Base Region ◽  
The South ◽  
North East ◽  
The North ◽  
Physico Chemical

&lt;p&gt;The geological extreme Dallol region, located around the Dallol volcano in the north-east of Danakil depression (Ethiopia), is considered as one of the harshest and hottest places on Earth. The geology is made up of years and years of evaporates accumulation. Volcanic activity generates ascending brines that may cross and mix with aquifers from inflowing meteoric water originating from the Ethiopian highlands on the east of the Danakil depression. When these mixtures reach the surface they can generate hydrothermal springs giving rise to waterbodies in the form of small ponds or lakes. During the Europlanet 2018 Danakil field expedition, ten of these saline waterbodies were extensively studied by &lt;em&gt;in situ&lt;/em&gt; measurements and &lt;em&gt;ex situ&lt;/em&gt; geo&amp;#8211;physico-chemical and &amp;#8211;microbiological analyses of collected samples, liquids as well as sediments.&lt;/p&gt;&lt;p&gt;The &lt;em&gt;in situ&lt;/em&gt; physico-chemical measurements clearly indicated the extreme nature of all ten investigated lakes. Laboratory analyses of the collected batch samples of liquids and sediments confirmed the extreme character of the waterbodies and complements our geological survey of the region with valuable geo&amp;#8211;chemical and &amp;#8211;microbiological data.&lt;/p&gt;&lt;p&gt;Based on our analytical results, the relative small Dallol region can still be subdivided into three geological smaller areas: the outcrop zone, the volcanic base region and the distant south area. The outcrop zone is dominated by sodium, iron and potassium. Oxidation processes in the outflowing superheated ferrous and sulfidic rich brine give rise to some of the most acidic ponds on our planet. In the ponds and lakes of the volcanic base region, incredible high amounts of calcium and/or magnesium can remain in their dissolved form as the most dominant and quasi only available anion is chloride. This region is host for the most saline water body on Earth. Chemical analysis of the lakes of the distant south area show that sodium is by far the most dominant cation. It is therefore no surprise that the large Karum Lake in the south region is economically exploited for the mining of sodium chloride.&lt;/p&gt;&lt;p&gt;Our mineralogy analyses render results that are completely in line with the observed geochemistry of the waterbodies. Halite and sylvite are the most present minerals in the Dallol outcrop zone associated with some gypsum and in one case with anhydrite. The geology around the waterbodies of volcanic base zone are a little bit more divers. On the shores of the Gaet&amp;#8217;ale Pond tachyhydrite, chloromagnesite, halite and sylvite is determined, while the Black Lake is surrounded by bischofite and carnalite. Logically, the mineralogy of the south area, the salt mining area, is dominated by halite and sylvite.&lt;/p&gt;&lt;p&gt;Apparently, the geochemistry of the outcrop zone and volcanic base region is so harsh that no extremophilic organism is able to survive in these areas. Only in the distant south area did we find indications of the presence of halophiles. Besides the bacterial genus &lt;em&gt;Salinibacter&lt;/em&gt;, our 16S rDNA microbiological fingerprinting indicates the presence of halophilic archaea like:&amp;#160; &lt;em&gt;Halobaculum sp., Halobellus sp., Halomicroarcula sp., Halorientalis sp.&lt;/em&gt; with the majority of the population being &lt;em&gt;Candidatus Nanosalina sp&lt;/em&gt;.&lt;/p&gt;

scholarly journals On the spatial segregation of helicity by inertial waves in dynamo simulations and planetary cores

2018 ◽  
Vol 851 ◽  
pp. 268-287 ◽  
Author(s):  
P. A. Davidson ◽  
A. Ranjan
Keyword(s):  
Numerical Simulations ◽  
Strongly Correlated ◽  
Inertial Waves ◽  
The South ◽  
The North ◽  
Planetary Cores ◽  
Local Wave ◽  
Wave Flux ◽  
The Relationship

The distribution of kinetic helicity in a dipolar planetary dynamo is central to the success of that dynamo. Motivated by the helicity distributions observed in numerical simulations of the Earth’s dynamo, we consider the relationship between the kinetic helicity, $h=\boldsymbol{u}\boldsymbol{\cdot }\unicode[STIX]{x1D735}\times \boldsymbol{u}$, and the buoyancy field that acts as a source of helicity, where $\boldsymbol{u}$ is velocity. We show that, in the absence of a magnetic field, helicity evolves in accordance with the equation $\unicode[STIX]{x2202}h/\unicode[STIX]{x2202}t=-\unicode[STIX]{x1D735}\boldsymbol{\cdot }\boldsymbol{F}+S_{h}$, where the flux, $\boldsymbol{F}$, represents the transport of helicity by inertial waves, and the helicity source, $S_{h}$, involves the product of the buoyancy and the velocity fields. In the numerical simulations it is observed that the helicity outside the tangent cylinder is predominantly negative in the north and positive in the south, a feature which the authors had previously attributed to the transport of helicity by waves (Davidson & Ranjan, Geophys. J. Intl, vol. 202, 2015, pp. 1646–1662). It is also observed that there is a strong spatial correlation between the distribution of $h$ and of $S_{h}$, with $S_{h}$ also predominantly negative in the north and positive in the south. This correlation tentatively suggests that it is the in situ generation of helicity by buoyancy that establishes the distribution of $h$ outside the tangent cylinder, rather than the dispersal of helicity by waves, as had been previously argued by the authors. However, although $h$ and $S_{h}$ are strongly correlated, there is no such correlation between $\unicode[STIX]{x2202}h/\unicode[STIX]{x2202}t$ and $S_{h}$, as might be expected if the distribution of $h$ were established by an in situ generation mechanism. We explain these various observations by showing that inertial waves interact with the buoyancy field in such a way as to induce a source $S_{h}$ which has the same sign as the helicity in the local wave flux, and that the sign of $h$ is simply determined by the direction of that flux. We conclude that the observed distributions of $h$ and $S_{h}$ outside the tangent cylinder are consistent with the transport of helicity by waves.

scholarly journals Turbulence and hypoxia contribute to dense zooplankton scattering layers in Patagonian Fjord System

2017 ◽  
Author(s):  
Iván Pérez-Santos ◽  
Leonardo Castro ◽  
Nicolás Mayorga ◽  
Lauren Ross ◽  
Luis Cubillos ◽  
...  
Keyword(s):  
Water Column ◽  
Vertical Mixing ◽  
Acoustic Doppler Current Profiler ◽  
Eddy Diffusivity ◽  
Future Research ◽  
Dense Layer ◽  
The North ◽  
Diel Vertical Migrations ◽  
And Migration

Abstract. The Puyuhuapi Fjord is an atypical fjord, with two mouths, located in northern Patagonia (44.7° S). One mouth lies to the south, close to the Pacific Ocean, whilst the second connects with the Jacaf Channel to the north where a shallow sill inhibits deep water ventilation contributing to the hypoxic conditions below ~ 100 m depth. Acoustic Doppler Current Profiler moorings, scientific echo sounder transects, and in-situ abundance measurements were used to study zooplankton assemblages and migration patterns along Puyuhuapi Fjord and Jacaf Channel. The acoustic records and in-situ zooplankton data revealed diel vertical migrations of siphonophores, euphausiids and copepods. A dense layer of zooplankton was observed along Puyuhuapi Fjord between the surface and the top of the hypoxic layer (~ 100 m), which acted as a physic-chemical barrier to the distribution and migration of the zooplankton. Aggregations of zooplankton and fishes were generally more abundant around the sill in Jacaf Channel than anywhere within Puyuhuapi Fjord. In particular, zooplanktons were distributed throughout the entire water column to ~ 200 m depth, with no evidence of a hypoxic boundary. Turbulence measurements taken near the sill in the Jacaf Channel indicated high turbulent kinetic energy dissipation rates (ε ~ 10−4 W kg−1) and vertical diapycnal eddy diffusivity (Kρ ~ 10−2 m2 s−1) values. These elevated vertical mixing ensures that the water column well oxygenated and promotes zooplanktons aggregation. The sill region represents a major topographic contrast between the two fjords, and we suggest that this is an feature for future research on carbon export and fluxes in these fjords.

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