The phrase "a markedly negative" is correct and usable in written English.
It can be used to describe something that is significantly or noticeably negative in nature or impact.
Example: "The study revealed a markedly negative effect on the participants' mental health after prolonged exposure to the stressor."
Alternatives: "a significantly negative" or "a distinctly negative".
Our addiction to consuming is a vicious one, and it's having a markedly negative impact on virtually every aspect of our lives.
The conclusions are as follows: (1) The wind coming from mountains dispelled aerosols while the sea breeze invigorated aerosols, and the upwind showed a markedly negative relevance with AOD.
Bernanke said in April that the spending cuts due to sequestration and other measures had a markedly negative impact on the economy.
Bone metastases can have a markedly negative impact on skeletal health by disrupting normal bone metabolism and weakening the skeleton.
The A + T-rich region, the second and the third positions of PCGs on the J-strand have a markedly negative GC-skew, whereas a significantly biased positive GC-skew is present in the first codon positions of PCGs on both the J- and N-strands, in the third codon positions of PCGs on the N-strand, in rRNAs, and in tRNAs.
First, men's reliance on women's affect and attractiveness showed a markedly strong negative association (r = −0.73), suggesting that men focus either on women's nonverbal affective cues or on women's attractiveness when judging their momentary sexual interest, but not on both.
In overweight and obese subjects, a moderate dose of exercise induced a markedly greater negative energy balance than a higher dose (Rosenkilde et al. 2012).
The previously reported difference between the topologies of the global network and the network of essential yeast proteins is also evident, with the essential network displaying a markedly weaker negative correlation than the global network.
The public's assessment of the president's handling of both the economy and the war in Iraq was markedly negative.
Psychoanalytic theorists (Freudian psychologists) explain the genesis of the disorders in terms of markedly negative childhood experiences, such as abuse, that significantly alter the course of normal personality development.
Increased ventilation in the presence of obstructed airways is associated with markedly negative inspiratory pleural pressures.
