March 2023

This issue includes a look at hot vents along Gakkel Ridge, turbulence in the deep Mediterranean, an array of ocean education subjects, and more…

Oceanography | Vol. 36, No. 1

at 4,200 m depth is bounded by steep rift

valley walls and punctuated by a series

of axial volcanic ridges and smaller vol-

canic mounds (Michael et  al., 2003).

Edmonds et al. (2003) inferred the pres-

ence of an active hydrothermal vent site

from chemical data and assigned to a

small (1.5–2  km in diameter) volcanic

mound rising approximately 400 m from

the seafloor, at depths between 4,300 m

and 3,850 m (Figure 1b,c). A dredge from

south to north across this mound recov-

ered components of a sulfide chimney

in addition to abundant pillow basalts.

In parallel, in situ sensor data from a

MAPR (Miniature Autonomous Plume

Recorder) instrument attached to the

dredge revealed evidence for a turbid-

ity anomaly consistent with a nearby

source of active black smoker venting at a

depth of 2,800–3,400 m (Edmonds et al.,

2003; Michael et  al., 2003). During the

PS86 AURORA expedition, CTD profil-

ing, coupled with water column chemis-

try, revealed further evidence for ongoing

hydrothermal activity on the Aurora

mound (Boetius, 2015; German et  al.,

2022a). Seabed surveys with the Ocean

Floor Observation System (OFOS) deep-

tow camera across the summit from

north to south revealed deep rifts through

the thick sedimented seafloor across the

base of the volcanic mound. This imag-

ing, paired with CTD data, led to the first

imaging of an active black smoker on

Gakkel Ridge at 82°53.83'N, 6°15.32'W,

at ~3,900 m depth, on what was named

the Aurora Vent Field (AVF; Boetius,

2015; German et al., 2022a). The OFOS

surveys showed that the Aurora mound

has steep vertical basalt walls intermixed

with lower angle, sediment-draped steps.

The top of the mound is flat and sediment

covered, and the observed fauna con-

sisted of high abundances of filter feeders,

mostly glass sponges and anemones, and

at least two species of shrimp. Ophiuroids,

swimming polychaetes, and crustaceans

(potentially isopods) were also observed.

At the active vent site, bacterial mats and

small gastropods and amphipods were

observed (Boetius, 2015). The physico-

chemical and microbiological character-

ization of the huge buoyant vent plume

hovering above the AVF showed evidence

for venting fluids enriched in meth-

ane, and possibly hydrogen, fueling high

microbial activity in the plume (German

et al., 2022a; Massimiliano Molari, Max

Planck Institute for Marine Microbiology,

pers. comm., 2022). Due to the lack of a

deep-diving remotely operated vehicle

(ROV), however, no physical samples of

fluids, rocks, microbes, or animals could

be collected from the vent field.

In 2019, the Hot Vents in an Ice-

Covered Ocean (HACON19) cruise on

R/V Kronprins Haakon returned to the

Aurora mound, with the aim of conduct-

ing a multidisciplinary survey of the sea-

floor ecosystems centered around the

coordinates of the black smoker iden-

tified in 2014 by the PS86 Aurora team

(Boetius, 2015). This cruise obtained

new visual data of the AVF with the

towed Ocean Floor Observation and

Bathymetry System (OFOBS; Purser

et al., 2019; German et al., 2022a), con-

firming the presence of at least three black

smokers colonized by sparse fauna com-

posed of mostly gastropods and amphi-

pods (Bünz et  al., 2019). In addition, a

wealth of samples on the sedimented sur-

face of the Aurora mound were collected,

Gakkel Ridge

Greenland

Svalbard

FIGURE 1. (a) Map of the Gakkel Ridge in the Central Arctic Ocean with known hydrothermal plume

signals indicated by yellow stars (from Edmond et al., 2003) and the Aurora Vent Field marked with

a red star. (b) A red triangle locates the Aurora Vent Field within the Aurora mound based on pre-

vious bathymetry from the AMORE and AURORA/AWI expeditions. (c) The Aurora Vent Field (red

triangle) is shown against multibeam bathymetry of the Aurora mound based on bathymetry from

the HACON19 and HACON21 expeditions.

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